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Date: Tue, 20 Nov 2012 20:24:56 -0200
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc: Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/5] KVM: MMU: simplify set_spte
On Mon, Nov 05, 2012 at 08:11:03PM +0800, Xiao Guangrong wrote:
> It is more cleaner if we can update pte_access fist then set spte according
> to pte_access, also introduce gfn_need_write_protect to check whether the
> gfn need to be write-protected
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Please separate patch in:
- code movement with no logical modification.
- logical modification (such as condition for mark_page_dirty).
- move code to helper functions.
> arch/x86/kvm/mmu.c | 109 ++++++++++++++++++++++++++++++++--------------------
> 1 files changed, 67 insertions(+), 42 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 4ea731e..49957df 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2329,6 +2329,63 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
> return 0;
> }
>
> +static bool gfn_need_write_protect(struct kvm_vcpu *vcpu, u64 *sptep,
> + int level, gfn_t gfn, bool can_unsync)
> +{
> + /*
> + * Optimization: for pte sync, if spte was writable the hash
> + * lookup is unnecessary (and expensive). Write protection
> + * is responsibility of mmu_get_page / kvm_sync_page.
> + * Same reasoning can be applied to dirty page accounting.
> + */
> + if (!can_unsync && is_writable_pte(*sptep))
> + return false;
> +
> + if ((level > PT_PAGE_TABLE_LEVEL &&
> + has_wrprotected_page(vcpu->kvm, gfn, level)) ||
> + mmu_need_write_protect(vcpu, gfn, can_unsync))
> + return true;
> +
> + return false;
> +}
> +
> +/* The return value indicates whether the @gfn need to be write protected. */
> +static bool vcpu_adjust_access(struct kvm_vcpu *vcpu, u64 *sptep,
> + unsigned *pte_access, int user_fault,
> + int write_fault, int level, gfn_t gfn,
> + bool can_unsync, bool host_writable)
> +{
> + bool ret = false;
> + unsigned access = *pte_access;
> +
> + if (!host_writable)
> + access &= ~ACC_WRITE_MASK;
> +
> + if (!(access & ACC_WRITE_MASK) && (!vcpu->arch.mmu.direct_map &&
> + write_fault && !is_write_protection(vcpu) && !user_fault)) {
> + access |= ACC_WRITE_MASK;
> + access &= ~ACC_USER_MASK;
> +
> + /*
> + * If we converted a user page to a kernel page,
> + * so that the kernel can write to it when cr0.wp=0,
> + * then we should prevent the kernel from executing it
> + * if SMEP is enabled.
> + */
> + if (kvm_read_cr4_bits(vcpu, X86_CR4_SMEP))
> + access &= ~ACC_EXEC_MASK;
> + }
> +
> + if ((access & ACC_WRITE_MASK) &&
> + gfn_need_write_protect(vcpu, sptep, level, gfn, can_unsync)) {
> + access &= ~ACC_WRITE_MASK;
> + ret = true;
> + }
> +
> + *pte_access = access;
> + return ret;
> +}
> +
> static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> unsigned pte_access, int user_fault,
> int write_fault, int level,
> @@ -2341,6 +2398,9 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> if (set_mmio_spte(sptep, gfn, pfn, pte_access))
> return 0;
>
> + ret = vcpu_adjust_access(vcpu, sptep, &pte_access, user_fault,
> + write_fault, level, gfn, can_unsync, host_writable);
> +
> spte = PT_PRESENT_MASK;
> if (!speculative)
> spte |= shadow_accessed_mask;
> @@ -2353,61 +2413,26 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> if (pte_access & ACC_USER_MASK)
> spte |= shadow_user_mask;
>
> + if (pte_access & ACC_WRITE_MASK) {
> + spte |= PT_WRITABLE_MASK;
> + spte |= SPTE_MMU_WRITEABLE;
> + }
> +
> if (level > PT_PAGE_TABLE_LEVEL)
> spte |= PT_PAGE_SIZE_MASK;
> +
> if (tdp_enabled)
> spte |= kvm_x86_ops->get_mt_mask(vcpu, gfn,
> kvm_is_mmio_pfn(pfn));
>
> if (host_writable)
> spte |= SPTE_HOST_WRITEABLE;
> - else
> - pte_access &= ~ACC_WRITE_MASK;
>
> spte |= (u64)pfn << PAGE_SHIFT;
>
> - if ((pte_access & ACC_WRITE_MASK)
> - || (!vcpu->arch.mmu.direct_map && write_fault
> - && !is_write_protection(vcpu) && !user_fault)) {
> - spte |= PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE;
> -
> - if (!vcpu->arch.mmu.direct_map
> - && !(pte_access & ACC_WRITE_MASK)) {
> - spte &= ~PT_USER_MASK;
> - /*
> - * If we converted a user page to a kernel page,
> - * so that the kernel can write to it when cr0.wp=0,
> - * then we should prevent the kernel from executing it
> - * if SMEP is enabled.
> - */
> - if (kvm_read_cr4_bits(vcpu, X86_CR4_SMEP))
> - spte |= PT64_NX_MASK;
> - }
> -
> - /*
> - * Optimization: for pte sync, if spte was writable the hash
> - * lookup is unnecessary (and expensive). Write protection
> - * is responsibility of mmu_get_page / kvm_sync_page.
> - * Same reasoning can be applied to dirty page accounting.
> - */
> - if (!can_unsync && is_writable_pte(*sptep))
> - goto set_pte;
> -
> - if ((level > PT_PAGE_TABLE_LEVEL &&
> - has_wrprotected_page(vcpu->kvm, gfn, level)) ||
> - mmu_need_write_protect(vcpu, gfn, can_unsync)) {
> - pgprintk("%s: found shadow page for %llx, marking ro\n",
> - __func__, gfn);
> - ret = 1;
> - pte_access &= ~ACC_WRITE_MASK;
> - spte &= ~(PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE);
> - }
> - }
> -
> - if (pte_access & ACC_WRITE_MASK)
> + if (is_writable_pte(spte))
> mark_page_dirty(vcpu->kvm, gfn);
>
> -set_pte:
> if (mmu_spte_update(sptep, spte))
> kvm_flush_remote_tlbs(vcpu->kvm);
> return ret;
> --
> 1.7.7.6
>
> --
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