Re: [PATCH v3 01/15] KVM: MMU: properly check last spte in fast_page_fault()

Marcelo Tosatti
2013-11-12T00:26:27Z

On Wed, Oct 23, 2013 at 09:29:19PM +0800, Xiao Guangrong wrote:
> Using sp->role.level instead of @level since @level is not got from the
> page table hierarchy
>
> There is no issue in current code since the fast page fault currently only
> fixes the fault caused by dirty-log that is always on the last level
> (level = 1)
>
> This patch makes the code more readable and avoids potential issue in the
> further development
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> ---
> arch/x86/kvm/mmu.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 40772ef..d2aacc2 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2798,9 +2798,9 @@ static bool page_fault_can_be_fast(u32 error_code)
> }
>
> static bool
> -fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 spte)
> +fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> + u64 *sptep, u64 spte)
> {
> - struct kvm_mmu_page *sp = page_header(__pa(sptep));
> gfn_t gfn;
>
> WARN_ON(!sp->role.direct);
> @@ -2826,6 +2826,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
> u32 error_code)
> {
> struct kvm_shadow_walk_iterator iterator;
> + struct kvm_mmu_page *sp;
> bool ret = false;
> u64 spte = 0ull;
>
> @@ -2846,7 +2847,8 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
> goto exit;
> }
>
> - if (!is_last_spte(spte, level))
> + sp = page_header(__pa(iterator.sptep));
> + if (!is_last_spte(spte, sp->role.level))
> goto exit;
>
> /*
> @@ -2872,7 +2874,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
> * the gfn is not stable for indirect shadow page.
> * See Documentation/virtual/kvm/locking.txt to get more detail.
> */
> - ret = fast_pf_fix_direct_spte(vcpu, iterator.sptep, spte);
> + ret = fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte);
> exit:
> trace_fast_page_fault(vcpu, gva, error_code, iterator.sptep,
> spte, ret);
> --
> 1.8.1.4

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>