On server-class POWER machines, we don't need the SWIOTLB unless we're a
secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
allocate it.
In most cases this is harmless, but on a few machine configurations (e.g.,
POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
fails with a scary-looking WARN_ONCE:
------------[ cut here ]------------
memblock: bottom-up allocation failed, memory hotremove may be affected
WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
CFAR: c00000000014b7b4 IRQMASK: 1
GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
Call Trace:
[c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
[c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
[c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
[c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
[c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
[c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
[c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
[c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
Instruction dump:
2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
---[ end trace 0000000000000000 ]---
software IO TLB: Cannot allocate buffer
Unless this is a secure VM the message can actually be ignored, because the
SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
Fixes: eae9eec476d1 ("powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory")
Signed-off-by: Thiago Jung Bauermann <[email protected]>
---
arch/powerpc/mm/mem.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index afab328d0887..3af991844145 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -300,7 +300,8 @@ void __init mem_init(void)
memblock_set_bottom_up(true);
if (is_secure_guest())
svm_swiotlb_init();
- else
+ /* Server machines don't need SWIOTLB if they're not secure guests. */
+ else if (!machine_is(pseries) && !machine_is(powernv))
swiotlb_init(0);
#endif
On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote:
> On server-class POWER machines, we don't need the SWIOTLB unless we're a
> secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
> allocate it.
>
> In most cases this is harmless, but on a few machine configurations (e.g.,
> POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
> happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
> fails with a scary-looking WARN_ONCE:
>
> ------------[ cut here ]------------
> memblock: bottom-up allocation failed, memory hotremove may be affected
> WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
> NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
> REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
> MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
> CFAR: c00000000014b7b4 IRQMASK: 1
> GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
> GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
> GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
> GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
> GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
> GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
> GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
> NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
> LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
> Call Trace:
> [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
> [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
> [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
> [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
> [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
> [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
> [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
> [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
> Instruction dump:
> 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
> 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
> random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
> ---[ end trace 0000000000000000 ]---
> software IO TLB: Cannot allocate buffer
>
> Unless this is a secure VM the message can actually be ignored, because the
> SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
The above warn_on is conveying a genuine warning. Should it be silenced?
>
> Fixes: eae9eec476d1 ("powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory")
> Signed-off-by: Thiago Jung Bauermann <[email protected]>
> ---
> arch/powerpc/mm/mem.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index afab328d0887..3af991844145 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -300,7 +300,8 @@ void __init mem_init(void)
> memblock_set_bottom_up(true);
> if (is_secure_guest())
> svm_swiotlb_init();
> - else
> + /* Server machines don't need SWIOTLB if they're not secure guests. */
> + else if (!machine_is(pseries) && !machine_is(powernv))
I can see powernv never needing SWIOTLB. But, pseries guests, I am not
so sure.
RP
Hi Ram,
Thanks for reviewing this patch.
Ram Pai <[email protected]> writes:
> On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote:
>> On server-class POWER machines, we don't need the SWIOTLB unless we're a
>> secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
>> allocate it.
>>
>> In most cases this is harmless, but on a few machine configurations (e.g.,
>> POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
>> happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
>> fails with a scary-looking WARN_ONCE:
>>
>> ------------[ cut here ]------------
>> memblock: bottom-up allocation failed, memory hotremove may be affected
>> WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
>> Modules linked in:
>> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
>> NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
>> REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
>> MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
>> CFAR: c00000000014b7b4 IRQMASK: 1
>> GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
>> GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
>> GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
>> GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
>> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
>> GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
>> GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
>> GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
>> NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
>> LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
>> Call Trace:
>> [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
>> [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
>> [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
>> [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
>> [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
>> [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
>> [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
>> [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
>> Instruction dump:
>> 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
>> 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
>> random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
>> ---[ end trace 0000000000000000 ]---
>> software IO TLB: Cannot allocate buffer
>>
>> Unless this is a secure VM the message can actually be ignored, because the
>> SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
>
> The above warn_on is conveying a genuine warning. Should it be silenced?
Not sure I understand your point. This patch doesn't silence the
warning, it avoids the problem it is warning about.
In any case, there's another patch being submitted upstream which
actually removes the warning by improving memblock's search for a free
memory region:
https://lore.kernel.org/lkml/[email protected]/
>>
>> Fixes: eae9eec476d1 ("powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory")
>> Signed-off-by: Thiago Jung Bauermann <[email protected]>
>> ---
>> arch/powerpc/mm/mem.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
>> index afab328d0887..3af991844145 100644
>> --- a/arch/powerpc/mm/mem.c
>> +++ b/arch/powerpc/mm/mem.c
>> @@ -300,7 +300,8 @@ void __init mem_init(void)
>> memblock_set_bottom_up(true);
>> if (is_secure_guest())
>> svm_swiotlb_init();
>> - else
>> + /* Server machines don't need SWIOTLB if they're not secure guests. */
>> + else if (!machine_is(pseries) && !machine_is(powernv))
>
> I can see powernv never needing SWIOTLB. But, pseries guests, I am not
> so sure.
We've just very recently enabled CONFIG_SWIOTLB on production pseries
kernel configs. So far it hasn't been needed except for SVMs.
--
Thiago Jung Bauermann
IBM Linux Technology Center
On Wed, Dec 23, 2020 at 09:06:01PM -0300, Thiago Jung Bauermann wrote:
>
> Hi Ram,
>
> Thanks for reviewing this patch.
>
> Ram Pai <[email protected]> writes:
>
> > On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote:
> >> On server-class POWER machines, we don't need the SWIOTLB unless we're a
> >> secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
> >> allocate it.
> >>
> >> In most cases this is harmless, but on a few machine configurations (e.g.,
> >> POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
> >> happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
> >> fails with a scary-looking WARN_ONCE:
> >>
> >> ------------[ cut here ]------------
> >> memblock: bottom-up allocation failed, memory hotremove may be affected
> >> WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
> >> Modules linked in:
> >> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
> >> NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
> >> REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
> >> MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
> >> CFAR: c00000000014b7b4 IRQMASK: 1
> >> GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
> >> GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
> >> GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
> >> GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
> >> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
> >> GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
> >> GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
> >> GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
> >> NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
> >> LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
> >> Call Trace:
> >> [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
> >> [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
> >> [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
> >> [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
> >> [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
> >> [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
> >> [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
> >> [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
> >> Instruction dump:
> >> 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
> >> 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
> >> random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
> >> ---[ end trace 0000000000000000 ]---
> >> software IO TLB: Cannot allocate buffer
> >>
> >> Unless this is a secure VM the message can actually be ignored, because the
> >> SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
> >
> > The above warn_on is conveying a genuine warning. Should it be silenced?
>
> Not sure I understand your point. This patch doesn't silence the
> warning, it avoids the problem it is warning about.
Sorry, I should have explained it better. My point is...
If CONFIG_SWIOTLB is enabled, it means that the kernel is
promising the bounce buffering capability. I know, currently we
do not have any kernel subsystems that use bounce buffers on
non-secure-pseries-kernel or powernv-kernel. But that does not
mean, there wont be any. In case there is such a third-party
module needing bounce buffering, it wont be able to operate,
because of the proposed change in your patch.
Is that a good thing or a bad thing, I do not know. I will let
the experts opine.
RP
Ram Pai <[email protected]> writes:
> On Wed, Dec 23, 2020 at 09:06:01PM -0300, Thiago Jung Bauermann wrote:
>>
>> Hi Ram,
>>
>> Thanks for reviewing this patch.
>>
>> Ram Pai <[email protected]> writes:
>>
>> > On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote:
>> >> On server-class POWER machines, we don't need the SWIOTLB unless we're a
>> >> secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
>> >> allocate it.
>> >>
>> >> In most cases this is harmless, but on a few machine configurations (e.g.,
>> >> POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
>> >> happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
>> >> fails with a scary-looking WARN_ONCE:
>> >>
>> >> ------------[ cut here ]------------
>> >> memblock: bottom-up allocation failed, memory hotremove may be affected
>> >> WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
>> >> Modules linked in:
>> >> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
>> >> NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
>> >> REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
>> >> MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
>> >> CFAR: c00000000014b7b4 IRQMASK: 1
>> >> GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
>> >> GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
>> >> GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
>> >> GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
>> >> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
>> >> GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
>> >> GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
>> >> GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
>> >> NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
>> >> LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
>> >> Call Trace:
>> >> [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
>> >> [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
>> >> [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
>> >> [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
>> >> [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
>> >> [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
>> >> [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
>> >> [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
>> >> Instruction dump:
>> >> 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
>> >> 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
>> >> random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
>> >> ---[ end trace 0000000000000000 ]---
>> >> software IO TLB: Cannot allocate buffer
>> >>
>> >> Unless this is a secure VM the message can actually be ignored, because the
>> >> SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
>> >
>> > The above warn_on is conveying a genuine warning. Should it be silenced?
>>
>> Not sure I understand your point. This patch doesn't silence the
>> warning, it avoids the problem it is warning about.
>
> Sorry, I should have explained it better. My point is...
>
> If CONFIG_SWIOTLB is enabled, it means that the kernel is
> promising the bounce buffering capability. I know, currently we
> do not have any kernel subsystems that use bounce buffers on
> non-secure-pseries-kernel or powernv-kernel. But that does not
> mean, there wont be any. In case there is such a third-party
> module needing bounce buffering, it wont be able to operate,
> because of the proposed change in your patch.
>
> Is that a good thing or a bad thing, I do not know. I will let
> the experts opine.
Ping? Does anyone else has an opinion on this? The other option I can
think of is changing the crashkernel code to not reserve so much memory
below 4 GB. Other people are considering this option, but it's not
planned for the near future.
Also, there's a patch currently in linux-next which removes the scary
warning because of unrelated reasons:
https://lore.kernel.org/lkml/[email protected]
So assuming that the patch above goes in and keeping the assumption that
the swiotlb won't be needed in the powernv machines where I've seen the
warning happen, we can just leave things as they are now.
--
Thiago Jung Bauermann
IBM Linux Technology Center
On Fri, Jan 08, 2021 at 09:27:01PM -0300, Thiago Jung Bauermann wrote:
>
> Ram Pai <[email protected]> writes:
>
> > On Wed, Dec 23, 2020 at 09:06:01PM -0300, Thiago Jung Bauermann wrote:
> >>
> >> Hi Ram,
> >>
> >> Thanks for reviewing this patch.
> >>
> >> Ram Pai <[email protected]> writes:
> >>
> >> > On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote:
> >> >> On server-class POWER machines, we don't need the SWIOTLB unless we're a
> >> >> secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
> >> >> allocate it.
> >> >>
> >> >> In most cases this is harmless, but on a few machine configurations (e.g.,
> >> >> POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
> >> >> happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
> >> >> fails with a scary-looking WARN_ONCE:
> >> >>
> >> >> ------------[ cut here ]------------
> >> >> memblock: bottom-up allocation failed, memory hotremove may be affected
> >> >> WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
> >> >> Modules linked in:
> >> >> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
> >> >> NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
> >> >> REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
> >> >> MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
> >> >> CFAR: c00000000014b7b4 IRQMASK: 1
> >> >> GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
> >> >> GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
> >> >> GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
> >> >> GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
> >> >> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
> >> >> GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
> >> >> GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
> >> >> GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
> >> >> NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
> >> >> LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
> >> >> Call Trace:
> >> >> [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
> >> >> [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
> >> >> [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
> >> >> [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
> >> >> [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
> >> >> [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
> >> >> [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
> >> >> [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
> >> >> Instruction dump:
> >> >> 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
> >> >> 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
> >> >> random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
> >> >> ---[ end trace 0000000000000000 ]---
> >> >> software IO TLB: Cannot allocate buffer
> >> >>
> >> >> Unless this is a secure VM the message can actually be ignored, because the
> >> >> SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
> >> >
> >> > The above warn_on is conveying a genuine warning. Should it be silenced?
> >>
> >> Not sure I understand your point. This patch doesn't silence the
> >> warning, it avoids the problem it is warning about.
> >
> > Sorry, I should have explained it better. My point is...
> >
> > If CONFIG_SWIOTLB is enabled, it means that the kernel is
> > promising the bounce buffering capability. I know, currently we
> > do not have any kernel subsystems that use bounce buffers on
> > non-secure-pseries-kernel or powernv-kernel. But that does not
> > mean, there wont be any. In case there is such a third-party
> > module needing bounce buffering, it wont be able to operate,
> > because of the proposed change in your patch.
> >
> > Is that a good thing or a bad thing, I do not know. I will let
> > the experts opine.
>
> Ping? Does anyone else has an opinion on this? The other option I can
> think of is changing the crashkernel code to not reserve so much memory
> below 4 GB. Other people are considering this option, but it's not
> planned for the near future.
That seems a more suitable solution regardless, but there is always
the danger of not being enough or being too big.
There was some autocrashkernel allocation patches going around
for x86 and ARM that perhaps could be re-used?
>
> Also, there's a patch currently in linux-next which removes the scary
> warning because of unrelated reasons:
>
> https://lore.kernel.org/lkml/[email protected]
>
> So assuming that the patch above goes in and keeping the assumption that
> the swiotlb won't be needed in the powernv machines where I've seen the
> warning happen, we can just leave things as they are now.
If that solves the problem, then that is OK.
>
> --
> Thiago Jung Bauermann
> IBM Linux Technology Center
Konrad Rzeszutek Wilk <[email protected]> writes:
> On Fri, Jan 08, 2021 at 09:27:01PM -0300, Thiago Jung Bauermann wrote:
>>
>> Ram Pai <[email protected]> writes:
>>
>> > On Wed, Dec 23, 2020 at 09:06:01PM -0300, Thiago Jung Bauermann wrote:
>> >>
>> >> Hi Ram,
>> >>
>> >> Thanks for reviewing this patch.
>> >>
>> >> Ram Pai <[email protected]> writes:
>> >>
>> >> > On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote:
>> >> >> On server-class POWER machines, we don't need the SWIOTLB unless we're a
>> >> >> secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally
>> >> >> allocate it.
>> >> >>
>> >> >> In most cases this is harmless, but on a few machine configurations (e.g.,
>> >> >> POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can
>> >> >> happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and
>> >> >> fails with a scary-looking WARN_ONCE:
>> >> >>
>> >> >> ------------[ cut here ]------------
>> >> >> memblock: bottom-up allocation failed, memory hotremove may be affected
>> >> >> WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340
>> >> >> Modules linked in:
>> >> >> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6
>> >> >> NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080
>> >> >> REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+)
>> >> >> MSR: 9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE> CR: 28022222 XER: 20040000
>> >> >> CFAR: c00000000014b7b4 IRQMASK: 1
>> >> >> GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047
>> >> >> GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000
>> >> >> GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001
>> >> >> GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000
>> >> >> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000
>> >> >> GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10
>> >> >> GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890
>> >> >> GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff
>> >> >> NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340
>> >> >> LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340
>> >> >> Call Trace:
>> >> >> [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable)
>> >> >> [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0
>> >> >> [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110
>> >> >> [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc
>> >> >> [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104
>> >> >> [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98
>> >> >> [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8
>> >> >> [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58
>> >> >> Instruction dump:
>> >> >> 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60
>> >> >> 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000
>> >> >> random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0
>> >> >> ---[ end trace 0000000000000000 ]---
>> >> >> software IO TLB: Cannot allocate buffer
>> >> >>
>> >> >> Unless this is a secure VM the message can actually be ignored, because the
>> >> >> SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases.
>> >> >
>> >> > The above warn_on is conveying a genuine warning. Should it be silenced?
>> >>
>> >> Not sure I understand your point. This patch doesn't silence the
>> >> warning, it avoids the problem it is warning about.
>> >
>> > Sorry, I should have explained it better. My point is...
>> >
>> > If CONFIG_SWIOTLB is enabled, it means that the kernel is
>> > promising the bounce buffering capability. I know, currently we
>> > do not have any kernel subsystems that use bounce buffers on
>> > non-secure-pseries-kernel or powernv-kernel. But that does not
>> > mean, there wont be any. In case there is such a third-party
>> > module needing bounce buffering, it wont be able to operate,
>> > because of the proposed change in your patch.
>> >
>> > Is that a good thing or a bad thing, I do not know. I will let
>> > the experts opine.
>>
>> Ping? Does anyone else has an opinion on this? The other option I can
>> think of is changing the crashkernel code to not reserve so much memory
>> below 4 GB. Other people are considering this option, but it's not
>> planned for the near future.
>
> That seems a more suitable solution regardless, but there is always
> the danger of not being enough or being too big.
>
> There was some autocrashkernel allocation patches going around
> for x86 and ARM that perhaps could be re-used?
Do you mean this?
https://lore.kernel.org/lkml/[email protected]/
I agree it would be great to have crashkernel=auto upstream.
>> Also, there's a patch currently in linux-next which removes the scary
>> warning because of unrelated reasons:
>>
>> https://lore.kernel.org/lkml/[email protected]
>>
>> So assuming that the patch above goes in and keeping the assumption that
>> the swiotlb won't be needed in the powernv machines where I've seen the
>> warning happen, we can just leave things as they are now.
>
> If that solves the problem, then that is OK.
Awesome! Today Mike Rapoport mentioned that the patch above uncovers a
few issues with late memory reservations on on x86 that he is fixing:
https://lore.kernel.org/lkml/[email protected]/
So that would be the last piece of the puzzle.
--
Thiago Jung Bauermann
IBM Linux Technology Center