2013-09-06 14:59:34

by Boris Ostrovsky

Subject: [PATCH] xen/p2m: Don't call get_balloon_scratch_page() twice, keep interrupts disabled for multicalls

m2p_remove_override() calls get_balloon_scratch_page() in
MULTI_update_va_mapping() even though it already has pointer to this page from
the earlier call (in scratch_page). This second call doesn't have a matching
put_balloon_scratch_page() thus not restoring preempt count back. (Also, there
is no put_balloon_scratch_page() in the error path.)

In addition, the second multicall uses __xen_mc_entry() which does not disable
interrupts. Rearrange xen_mc_* calls to keep interrupts off while performing
multicalls.

Signed-off-by: Boris Ostrovsky <[email protected]>
---
arch/x86/xen/p2m.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 0d4ec35..8b901e8 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -990,10 +990,13 @@ int m2p_remove_override(struct page *page,
printk(KERN_WARNING "m2p_remove_override: "
"pfn %lx mfn %lx, failed to modify kernel mappings",
pfn, mfn);
+ put_balloon_scratch_page();
return -1;
}

- mcs = xen_mc_entry(
+ xen_mc_batch();
+
+ mcs = __xen_mc_entry(
sizeof(struct gnttab_unmap_and_replace));
unmap_op = mcs.args;
unmap_op->host_addr = kmap_op->host_addr;
@@ -1003,12 +1006,11 @@ int m2p_remove_override(struct page *page,
MULTI_grant_table_op(mcs.mc,
GNTTABOP_unmap_and_replace, unmap_op, 1);

- xen_mc_issue(PARAVIRT_LAZY_MMU);
-
mcs = __xen_mc_entry(0);
MULTI_update_va_mapping(mcs.mc, scratch_page_address,
- pfn_pte(page_to_pfn(get_balloon_scratch_page()),
+ pfn_pte(page_to_pfn(scratch_page),
PAGE_KERNEL_RO), 0);
+
xen_mc_issue(PARAVIRT_LAZY_MMU);

kmap_op->host_addr = 0;
--
1.8.3.1

2013-09-06 15:09:43

by Stefano Stabellini

Subject: Re: [PATCH] xen/p2m: Don't call get_balloon_scratch_page() twice, keep interrupts disabled for multicalls

On Fri, 6 Sep 2013, Boris Ostrovsky wrote:
> m2p_remove_override() calls get_balloon_scratch_page() in
> MULTI_update_va_mapping() even though it already has pointer to this page from
> the earlier call (in scratch_page). This second call doesn't have a matching
> put_balloon_scratch_page() thus not restoring preempt count back. (Also, there
> is no put_balloon_scratch_page() in the error path.)
>
> In addition, the second multicall uses __xen_mc_entry() which does not disable
> interrupts. Rearrange xen_mc_* calls to keep interrupts off while performing
> multicalls.
>
> Signed-off-by: Boris Ostrovsky <[email protected]>

Reviewed-by: Stefano Stabellini <[email protected]>


> arch/x86/xen/p2m.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 0d4ec35..8b901e8 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -990,10 +990,13 @@ int m2p_remove_override(struct page *page,
> printk(KERN_WARNING "m2p_remove_override: "
> "pfn %lx mfn %lx, failed to modify kernel mappings",
> pfn, mfn);
> + put_balloon_scratch_page();
> return -1;
> }
>
> - mcs = xen_mc_entry(
> + xen_mc_batch();
> +
> + mcs = __xen_mc_entry(
> sizeof(struct gnttab_unmap_and_replace));
> unmap_op = mcs.args;
> unmap_op->host_addr = kmap_op->host_addr;
> @@ -1003,12 +1006,11 @@ int m2p_remove_override(struct page *page,
> MULTI_grant_table_op(mcs.mc,
> GNTTABOP_unmap_and_replace, unmap_op, 1);
>
> - xen_mc_issue(PARAVIRT_LAZY_MMU);
> -
> mcs = __xen_mc_entry(0);
> MULTI_update_va_mapping(mcs.mc, scratch_page_address,
> - pfn_pte(page_to_pfn(get_balloon_scratch_page()),
> + pfn_pte(page_to_pfn(scratch_page),
> PAGE_KERNEL_RO), 0);
> +
> xen_mc_issue(PARAVIRT_LAZY_MMU);
>
> kmap_op->host_addr = 0;
> --
> 1.8.3.1
>

2013-09-06 16:06:35

by Konrad Rzeszutek Wilk

Subject: Re: [PATCH] xen/p2m: Don't call get_balloon_scratch_page() twice, keep interrupts disabled for multicalls

On 9/6/2013 11:09 AM, Stefano Stabellini wrote:
> On Fri, 6 Sep 2013, Boris Ostrovsky wrote:
>> m2p_remove_override() calls get_balloon_scratch_page() in
>> MULTI_update_va_mapping() even though it already has pointer to this page from
>> the earlier call (in scratch_page). This second call doesn't have a matching
>> put_balloon_scratch_page() thus not restoring preempt count back. (Also, there
>> is no put_balloon_scratch_page() in the error path.)
>>
>> In addition, the second multicall uses __xen_mc_entry() which does not disable
>> interrupts. Rearrange xen_mc_* calls to keep interrupts off while performing
>> multicalls.
>>
>> Signed-off-by: Boris Ostrovsky <[email protected]>
You also might want to mention that this fixes the regression introduced
by ..
commit id <"title"
> Reviewed-by: Stefano Stabellini <[email protected]>
>
>
>> arch/x86/xen/p2m.c | 10 ++++++----
>> 1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
>> index 0d4ec35..8b901e8 100644
>> --- a/arch/x86/xen/p2m.c
>> +++ b/arch/x86/xen/p2m.c
>> @@ -990,10 +990,13 @@ int m2p_remove_override(struct page *page,
>> printk(KERN_WARNING "m2p_remove_override: "
>> "pfn %lx mfn %lx, failed to modify kernel mappings",
>> pfn, mfn);
>> + put_balloon_scratch_page();
>> return -1;
>> }
>>
>> - mcs = xen_mc_entry(
>> + xen_mc_batch();
>> +
>> + mcs = __xen_mc_entry(
>> sizeof(struct gnttab_unmap_and_replace));
>> unmap_op = mcs.args;
>> unmap_op->host_addr = kmap_op->host_addr;
>> @@ -1003,12 +1006,11 @@ int m2p_remove_override(struct page *page,
>> MULTI_grant_table_op(mcs.mc,
>> GNTTABOP_unmap_and_replace, unmap_op, 1);
>>
>> - xen_mc_issue(PARAVIRT_LAZY_MMU);
>> -
>> mcs = __xen_mc_entry(0);
>> MULTI_update_va_mapping(mcs.mc, scratch_page_address,
>> - pfn_pte(page_to_pfn(get_balloon_scratch_page()),
>> + pfn_pte(page_to_pfn(scratch_page),
>> PAGE_KERNEL_RO), 0);
>> +
>> xen_mc_issue(PARAVIRT_LAZY_MMU);
>>
>> kmap_op->host_addr = 0;
>> --
>> 1.8.3.1
>>