KVM: MMU: fix comment in kvm_mmu_zap_collapsible_spte
diff mbox

Message ID 552C91BA.1010703@linux.intel.com
State New, archived
Headers show

Commit Message

Xiao Guangrong April 14, 2015, 4:04 a.m. UTC
Soft mmu uses direct shadow page to fill guest large mapping with small pages
if huge mamping is disallowed on host. So zapping direct shadow page works well
both for soft mmu and hard mmu

Fix the comment to reflect this truth

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
  arch/x86/kvm/mmu.c | 8 +++++---
  1 file changed, 5 insertions(+), 3 deletions(-)

Comments

Paolo Bonzini April 15, 2015, 3:05 p.m. UTC | #1
> -         * Only EPT supported for now; otherwise, one would need to
> -         * find out efficiently whether the guest page tables are
> -         * also using huge pages.
> +         * We can not do huge page mapping for the indirect shadow
> +         * page (sp) found on the last rmap (level = 1 ) since
> +         * indirect sp is synced with the page table in guest and
> +         * indirect sp->level = 1 means the guest page table is
> +         * using 4K page size mapping.

What about:

+		 * We cannot do huge page mapping for indirect shadow pages,
+		 * which are found on the last rmap (level = 1) when not using
+		 * tdp; such shadow pages are synced with the page table in
+		 * the guest, and the guest page table is using 4K page size
+		 * mapping if the indirect sp has level = 1.
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Xiao Guangrong April 16, 2015, 12:38 a.m. UTC | #2
On 04/15/2015 11:05 PM, Paolo Bonzini wrote:
>
>
>> -         * Only EPT supported for now; otherwise, one would need to
>> -         * find out efficiently whether the guest page tables are
>> -         * also using huge pages.
>> +         * We can not do huge page mapping for the indirect shadow
>> +         * page (sp) found on the last rmap (level = 1 ) since
>> +         * indirect sp is synced with the page table in guest and
>> +         * indirect sp->level = 1 means the guest page table is
>> +         * using 4K page size mapping.
>
> What about:
>
> +		 * We cannot do huge page mapping for indirect shadow pages,
> +		 * which are found on the last rmap (level = 1) when not using
> +		 * tdp; such shadow pages are synced with the page table in
> +		 * the guest, and the guest page table is using 4K page size
> +		 * mapping if the indirect sp has level = 1.

Yeah, much better. Thanks for your improvement, Paolo!
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Wanpeng Li April 16, 2015, 8:14 a.m. UTC | #3
On Wed, Apr 15, 2015 at 05:05:48PM +0200, Paolo Bonzini wrote:
>
>
>> -         * Only EPT supported for now; otherwise, one would need to
>> -         * find out efficiently whether the guest page tables are
>> -         * also using huge pages.
>> +         * We can not do huge page mapping for the indirect shadow
>> +         * page (sp) found on the last rmap (level = 1 ) since
>> +         * indirect sp is synced with the page table in guest and
>> +         * indirect sp->level = 1 means the guest page table is
>> +         * using 4K page size mapping.
>
>What about:
>
>+		 * We cannot do huge page mapping for indirect shadow pages,
>+		 * which are found on the last rmap (level = 1) when not using
>+		 * tdp; such shadow pages are synced with the page table in
>+		 * the guest, and the guest page table is using 4K page size
>+		 * mapping if the indirect sp has level = 1.

Reviewed-by: Wanpeng Li <wanpeng.li@linux.intel.com>
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Patch
diff mbox

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 146f295..68c5487 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4481,9 +4481,11 @@  static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
  		pfn = spte_to_pfn(*sptep);

  		/*
-		 * Only EPT supported for now; otherwise, one would need to
-		 * find out efficiently whether the guest page tables are
-		 * also using huge pages.
+		 * We can not do huge page mapping for the indirect shadow
+		 * page (sp) found on the last rmap (level = 1 ) since
+		 * indirect sp is synced with the page table in guest and
+		 * indirect sp->level = 1 means the guest page table is
+		 * using 4K page size mapping.
  		 */
  		if (sp->role.direct &&
  			!kvm_is_reserved_pfn(pfn) &&