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Commit 72016f3a authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: MMU: Consolidate two guest pte reads in kvm_mmu_pte_write() 



kvm_mmu_pte_write() reads guest ptes in two different occasions, both to
allow a 32-bit pae guest to update a pte with 4-byte writes.  Consolidate
these into a single read, which also allows us to consolidate another read
from an invlpg speculating a gpte into the shadow page table.

Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent d57e2c07

arch/x86/kvm/mmu.c

+31 −38
Original line number Diff line number Diff line
@@ -2560,36 +2560,11 @@ static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu) 
}



static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,

					  const u8 *new, int bytes)

					  u64 gpte)

{

	gfn_t gfn;

	int r;

	u64 gpte = 0;

	pfn_t pfn;



	if (bytes != 4 && bytes != 8)

		return;



	/*

	 * Assume that the pte write on a page table of the same type

	 * as the current vcpu paging mode.  This is nearly always true

	 * (might be false while changing modes).  Note it is verified later

	 * by update_pte().

	 */

	if (is_pae(vcpu)) {

		/* Handle a 32-bit guest writing two halves of a 64-bit gpte */

		if ((bytes == 4) && (gpa % 4 == 0)) {

			r = kvm_read_guest(vcpu->kvm, gpa & ~(u64)7, &gpte, 8);

			if (r)

				return;

			memcpy((void *)&gpte + (gpa % 8), new, 4);

		} else if ((bytes == 8) && (gpa % 8 == 0)) {

			memcpy((void *)&gpte, new, 8);

		}

	} else {

		if ((bytes == 4) && (gpa % 4 == 0))

			memcpy((void *)&gpte, new, 4);

	}

	if (!is_present_gpte(gpte))

		return;

	gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
@@ -2640,7 +2615,34 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, 
	int r;



	pgprintk("%s: gpa %llx bytes %d\n", __func__, gpa, bytes);

	mmu_guess_page_from_pte_write(vcpu, gpa, new, bytes);



	switch (bytes) {

	case 4:

		gentry = *(const u32 *)new;

		break;

	case 8:

		gentry = *(const u64 *)new;

		break;

	default:

		gentry = 0;

		break;

	}



	/*

	 * Assume that the pte write on a page table of the same type

	 * as the current vcpu paging mode.  This is nearly always true

	 * (might be false while changing modes).  Note it is verified later

	 * by update_pte().

	 */

	if (is_pae(vcpu) && bytes == 4) {

		/* Handle a 32-bit guest writing two halves of a 64-bit gpte */

		gpa &= ~(gpa_t)7;

		r = kvm_read_guest(vcpu->kvm, gpa, &gentry, 8);

		if (r)

			gentry = 0;

	}



	mmu_guess_page_from_pte_write(vcpu, gpa, gentry);

	spin_lock(&vcpu->kvm->mmu_lock);

	kvm_mmu_access_page(vcpu, gfn);

	kvm_mmu_free_some_pages(vcpu);
@@ -2705,20 +2707,11 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa, 
				continue;

		}

		spte = &sp->spt[page_offset / sizeof(*spte)];

		if ((gpa & (pte_size - 1)) || (bytes < pte_size)) {

			gentry = 0;

			r = kvm_read_guest_atomic(vcpu->kvm,

						  gpa & ~(u64)(pte_size - 1),

						  &gentry, pte_size);

			new = (const void *)&gentry;

			if (r < 0)

				new = NULL;

		}

		while (npte--) {

			entry = *spte;

			mmu_pte_write_zap_pte(vcpu, sp, spte);

			if (new)

				mmu_pte_write_new_pte(vcpu, sp, spte, new);

			if (gentry)

				mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);

			mmu_pte_write_flush_tlb(vcpu, entry, *spte);

			++spte;

		}