Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 9b51a630 authored by Kai Huang's avatar Kai Huang Committed by Paolo Bonzini
Browse files

KVM: MMU: Explicitly set D-bit for writable spte. 



This patch avoids unnecessary dirty GPA logging to PML buffer in EPT violation
path by setting D-bit manually prior to the occurrence of the write from guest.

We only set D-bit manually in set_spte, and leave fast_page_fault path
unchanged, as fast_page_fault is very unlikely to happen in case of PML.

For the hva <-> pa change case, the spte is updated to either read-only (host
pte is read-only) or be dropped (host pte is writeable), and both cases will be
handled by above changes, therefore no change is necessary.

Signed-off-by: default avatarKai Huang <kai.huang@linux.intel.com>
Reviewed-by: default avatarXiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f4b4b180

arch/x86/kvm/mmu.c

+15 −1
Original line number Diff line number Diff line
@@ -2597,8 +2597,10 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, 
		}

	}



	if (pte_access & ACC_WRITE_MASK)

	if (pte_access & ACC_WRITE_MASK) {

		mark_page_dirty(vcpu->kvm, gfn);

		spte |= shadow_dirty_mask;

	}



set_pte:

	if (mmu_spte_update(sptep, spte))
@@ -2914,6 +2916,18 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, 
	 */

	gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);



	/*

	 * Theoretically we could also set dirty bit (and flush TLB) here in

	 * order to eliminate unnecessary PML logging. See comments in

	 * set_spte. But fast_page_fault is very unlikely to happen with PML

	 * enabled, so we do not do this. This might result in the same GPA

	 * to be logged in PML buffer again when the write really happens, and

	 * eventually to be called by mark_page_dirty twice. But it's also no

	 * harm. This also avoids the TLB flush needed after setting dirty bit

	 * so non-PML cases won't be impacted.

	 *

	 * Compare with set_spte where instead shadow_dirty_mask is set.

	 */

	if (cmpxchg64(sptep, spte, spte | PT_WRITABLE_MASK) == spte)

		mark_page_dirty(vcpu->kvm, gfn);