kernel crash was observed because of page fault, while running
cpuhotplug ltp testcases on SEV-ES enabled systems. The crash was
observed during hotplug after the CPU was offlined and the process
was migrated to different cpu. setup_ghcb() is called again which
tries to update ghcb_version in sev_es_negotiate_protocol(). Ideally this
is a read_only variable which is initialised during booting.
This results in pagefault.
From logs,
[ 256.447466] BUG: unable to handle page fault for address: ffffffffba556e70
[ 256.447476] #PF: supervisor write access in kernel mode
[ 256.447478] #PF: error_code(0x0003) - permissions violation
[ 256.447479] PGD 8000667c0f067 P4D 8000667c0f067 PUD 8000667c10063 PMD 80080006674001e1
[ 256.447483] Oops: 0003 [#1] PREEMPT SMP NOPTI
[ 256.447487] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.1.45-8.ph5 #1-photon
.
.
.
.
.
[ 256.447511] CR2: ffffffffba556e70 CR3: 0008000667c0a004 CR4: 0000000000770ee0
[ 256.447514] PKRU: 55555554
[ 256.447515] Call Trace:
[ 256.447516] <TASK>
[ 256.447519] ? __die_body.cold+0x1a/0x1f
[ 256.447526] ? __die+0x2a/0x35
[ 256.447528] ? page_fault_oops+0x10c/0x270
[ 256.447531] ? setup_ghcb+0x71/0x100
[ 256.447533] ? __x86_return_thunk+0x5/0x6
[ 256.447537] ? search_exception_tables+0x60/0x70
[ 256.447541] ? __x86_return_thunk+0x5/0x6
[ 256.447543] ? fixup_exception+0x27/0x320
[ 256.447546] ? kernelmode_fixup_or_oops+0xa2/0x120
[ 256.447549] ? __bad_area_nosemaphore+0x16a/0x1b0
[ 256.447551] ? kernel_exc_vmm_communication+0x60/0xb0
[ 256.447556] ? bad_area_nosemaphore+0x16/0x20
[ 256.447558] ? do_kern_addr_fault+0x7a/0x90
[ 256.447560] ? exc_page_fault+0xbd/0x160
[ 256.447563] ? asm_exc_page_fault+0x27/0x30
[ 256.447570] ? setup_ghcb+0x71/0x100
[ 256.447572] ? setup_ghcb+0xe/0x100
[ 256.447574] cpu_init_exception_handling+0x1b9/0x1f0
Fix is to avoid updating the variable after it has been initialised during booting.
Fixes: 95d33bfaa3e1 ("x86/sev: Register GHCB memory when SEV-SNP is active")
Signed-off-by: Ashwin Dayanand Kamat <[email protected]>
Co-developed-by: Bo Gan <[email protected]>
---
arch/x86/kernel/sev-shared.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index ccb0915e84e1..a447908f2b4d 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -144,6 +144,9 @@ static bool sev_es_negotiate_protocol(void)
{
u64 val;
+ if (ghcb_version)
+ return true;
+
/* Do the GHCB protocol version negotiation */
sev_es_wr_ghcb_msr(GHCB_MSR_SEV_INFO_REQ);
VMGEXIT();
--
2.39.0
On 11/6/23 00:32, Ashwin Dayanand Kamat wrote:
> kernel crash was observed because of page fault, while running
> cpuhotplug ltp testcases on SEV-ES enabled systems. The crash was
> observed during hotplug after the CPU was offlined and the process
> was migrated to different cpu. setup_ghcb() is called again which
> tries to update ghcb_version in sev_es_negotiate_protocol(). Ideally this
> is a read_only variable which is initialised during booting.
> This results in pagefault.
>
> From logs,
> [ 256.447466] BUG: unable to handle page fault for address: ffffffffba556e70
> [ 256.447476] #PF: supervisor write access in kernel mode
> [ 256.447478] #PF: error_code(0x0003) - permissions violation
> [ 256.447479] PGD 8000667c0f067 P4D 8000667c0f067 PUD 8000667c10063 PMD 80080006674001e1
> [ 256.447483] Oops: 0003 [#1] PREEMPT SMP NOPTI
> [ 256.447487] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.1.45-8.ph5 #1-photon
> .
> .
> .
> .
> .
> [ 256.447511] CR2: ffffffffba556e70 CR3: 0008000667c0a004 CR4: 0000000000770ee0
> [ 256.447514] PKRU: 55555554
> [ 256.447515] Call Trace:
> [ 256.447516] <TASK>
> [ 256.447519] ? __die_body.cold+0x1a/0x1f
> [ 256.447526] ? __die+0x2a/0x35
> [ 256.447528] ? page_fault_oops+0x10c/0x270
> [ 256.447531] ? setup_ghcb+0x71/0x100
> [ 256.447533] ? __x86_return_thunk+0x5/0x6
> [ 256.447537] ? search_exception_tables+0x60/0x70
> [ 256.447541] ? __x86_return_thunk+0x5/0x6
> [ 256.447543] ? fixup_exception+0x27/0x320
> [ 256.447546] ? kernelmode_fixup_or_oops+0xa2/0x120
> [ 256.447549] ? __bad_area_nosemaphore+0x16a/0x1b0
> [ 256.447551] ? kernel_exc_vmm_communication+0x60/0xb0
> [ 256.447556] ? bad_area_nosemaphore+0x16/0x20
> [ 256.447558] ? do_kern_addr_fault+0x7a/0x90
> [ 256.447560] ? exc_page_fault+0xbd/0x160
> [ 256.447563] ? asm_exc_page_fault+0x27/0x30
> [ 256.447570] ? setup_ghcb+0x71/0x100
> [ 256.447572] ? setup_ghcb+0xe/0x100
> [ 256.447574] cpu_init_exception_handling+0x1b9/0x1f0
>
> Fix is to avoid updating the variable after it has been initialised during booting.
The call to sev_es_negotiate_protocol() could be moved down to after the
initial_vc_handler if-check in setup_ghcb(). That would then put the call
to sev_es_negotiate_protocol() only in the BSP boot phase (and it only
needs be done once). Does doing that prevent the #PF for you?
>
> Fixes: 95d33bfaa3e1 ("x86/sev: Register GHCB memory when SEV-SNP is active")
> Signed-off-by: Ashwin Dayanand Kamat <[email protected]>
> Co-developed-by: Bo Gan <[email protected]>
This tag needs to be moved above your Signed-off-by: and it needs a
Signed-off-by: for the co-developer.
Thanks,
Tom
> ---
> arch/x86/kernel/sev-shared.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index ccb0915e84e1..a447908f2b4d 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -144,6 +144,9 @@ static bool sev_es_negotiate_protocol(void)
> {
> u64 val;
>
> + if (ghcb_version)
> + return true;
> +
> /* Do the GHCB protocol version negotiation */
> sev_es_wr_ghcb_msr(GHCB_MSR_SEV_INFO_REQ);
> VMGEXIT();
> On 28-Nov-2023, at 3:40 AM, Tom Lendacky <[email protected]> wrote:
>
> !! External Email
>
> On 11/6/23 00:32, Ashwin Dayanand Kamat wrote:
>> kernel crash was observed because of page fault, while running
>> cpuhotplug ltp testcases on SEV-ES enabled systems. The crash was
>> observed during hotplug after the CPU was offlined and the process
>> was migrated to different cpu. setup_ghcb() is called again which
>> tries to update ghcb_version in sev_es_negotiate_protocol(). Ideally this
>> is a read_only variable which is initialised during booting.
>> This results in pagefault.
>>
>> From logs,
>> [ 256.447466] BUG: unable to handle page fault for address: ffffffffba556e70
>> [ 256.447476] #PF: supervisor write access in kernel mode
>> [ 256.447478] #PF: error_code(0x0003) - permissions violation
>> [ 256.447479] PGD 8000667c0f067 P4D 8000667c0f067 PUD 8000667c10063 PMD 80080006674001e1
>> [ 256.447483] Oops: 0003 [#1] PREEMPT SMP NOPTI
>> [ 256.447487] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.1.45-8.ph5 #1-photon
>> .
>> .
>> .
>> .
>> .
>> [ 256.447511] CR2: ffffffffba556e70 CR3: 0008000667c0a004 CR4: 0000000000770ee0
>> [ 256.447514] PKRU: 55555554
>> [ 256.447515] Call Trace:
>> [ 256.447516] <TASK>
>> [ 256.447519] ? __die_body.cold+0x1a/0x1f
>> [ 256.447526] ? __die+0x2a/0x35
>> [ 256.447528] ? page_fault_oops+0x10c/0x270
>> [ 256.447531] ? setup_ghcb+0x71/0x100
>> [ 256.447533] ? __x86_return_thunk+0x5/0x6
>> [ 256.447537] ? search_exception_tables+0x60/0x70
>> [ 256.447541] ? __x86_return_thunk+0x5/0x6
>> [ 256.447543] ? fixup_exception+0x27/0x320
>> [ 256.447546] ? kernelmode_fixup_or_oops+0xa2/0x120
>> [ 256.447549] ? __bad_area_nosemaphore+0x16a/0x1b0
>> [ 256.447551] ? kernel_exc_vmm_communication+0x60/0xb0
>> [ 256.447556] ? bad_area_nosemaphore+0x16/0x20
>> [ 256.447558] ? do_kern_addr_fault+0x7a/0x90
>> [ 256.447560] ? exc_page_fault+0xbd/0x160
>> [ 256.447563] ? asm_exc_page_fault+0x27/0x30
>> [ 256.447570] ? setup_ghcb+0x71/0x100
>> [ 256.447572] ? setup_ghcb+0xe/0x100
>> [ 256.447574] cpu_init_exception_handling+0x1b9/0x1f0
>>
>> Fix is to avoid updating the variable after it has been initialised during booting.
>
> The call to sev_es_negotiate_protocol() could be moved down to after the
> initial_vc_handler if-check in setup_ghcb(). That would then put the call
> to sev_es_negotiate_protocol() only in the BSP boot phase (and it only
> needs be done once). Does doing that prevent the #PF for you?
>
Verified the change and it works fine. Updated the same in v2.
>>
>> Fixes: 95d33bfaa3e1 ("x86/sev: Register GHCB memory when SEV-SNP is active")
>> Signed-off-by: Ashwin Dayanand Kamat <[email protected]>
>> Co-developed-by: Bo Gan <[email protected]>
>
> This tag needs to be moved above your Signed-off-by: and it needs a
> Signed-off-by: for the co-developer.
>
Fixed in v2.
> Thanks,
> Tom
>
>> ---
>> arch/x86/kernel/sev-shared.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
>> index ccb0915e84e1..a447908f2b4d 100644
>> --- a/arch/x86/kernel/sev-shared.c
>> +++ b/arch/x86/kernel/sev-shared.c
>> @@ -144,6 +144,9 @@ static bool sev_es_negotiate_protocol(void)
>> {
>> u64 val;
>>
>> + if (ghcb_version)
>> + return true;
>> +
>> /* Do the GHCB protocol version negotiation */
>> sev_es_wr_ghcb_msr(GHCB_MSR_SEV_INFO_REQ);
>> VMGEXIT();
>
> !! External Email: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender.