Commit 0b3c9333 authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: MMU: Simplify spte fetch() function 



Partition the function into three sections:

- fetching indirect shadow pages (host_level > guest_level)
- fetching direct shadow pages (page_level < host_level <= guest_level)
- the final spte (page_level == host_level)

Instead of the current spaghetti.

A slight change from the original code is that we call validate_direct_spte()
more often: previously we called it only for gw->level, now we also call it for
lower levels.  The change should have no effect.

[xiao: fix regression caused by validate_direct_spte() called too late]

Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent 39c8c672

arch/x86/kvm/paging_tmpl.h

+49 −44
Original line number Diff line number Diff line
@@ -321,9 +321,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, 
	unsigned access = gw->pt_access;

	struct kvm_mmu_page *sp;

	u64 *sptep = NULL;

	int direct;

	gfn_t table_gfn;

	int level;

	int uninitialized_var(level);

	bool dirty = is_dirty_gpte(gw->ptes[gw->level - 1]);

	unsigned direct_access;

	struct kvm_shadow_walk_iterator iterator;
@@ -335,61 +333,68 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, 
	if (!dirty)

		direct_access &= ~ACC_WRITE_MASK;



	for_each_shadow_entry(vcpu, addr, iterator) {

	for (shadow_walk_init(&iterator, vcpu, addr);

	     shadow_walk_okay(&iterator) && iterator.level > gw->level;

	     shadow_walk_next(&iterator)) {

		gfn_t table_gfn;



		level = iterator.level;

		sptep = iterator.sptep;

		if (iterator.level == hlevel) {

			mmu_set_spte(vcpu, sptep, access,

				     gw->pte_access & access,

				     user_fault, write_fault,

				     dirty, ptwrite, level,

				     gw->gfn, pfn, false, true);

			break;

		}



		if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)

		    && level == gw->level)

			validate_direct_spte(vcpu, sptep, direct_access);



		drop_large_spte(vcpu, sptep);



		if (is_shadow_present_pte(*sptep))

			continue;



		if (level <= gw->level) {

			direct = 1;

			access = direct_access;



			/*

			 * It is a large guest pages backed by small host pages,

			 * So we set @direct(@sp->role.direct)=1, and set

			 * @table_gfn(@sp->gfn)=the base page frame for linear

			 * translations.

			 */

			table_gfn = gw->gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);

			access &= gw->pte_access;

		} else {

			direct = 0;

		table_gfn = gw->table_gfn[level - 2];

		}

		sp = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,

					       direct, access, sptep);

		if (!direct)

				      false, access, sptep);



		/*

		 * Verify that the gpte in the page we've just write

		 * protected is still there.

		 */

			if (FNAME(gpte_changed)(vcpu, gw, level - 1)) {

				kvm_mmu_put_page(sp, sptep);

				kvm_release_pfn_clean(pfn);

				sptep = NULL;

				break;

		if (FNAME(gpte_changed)(vcpu, gw, level - 1))

			goto out_gpte_changed;



		link_shadow_page(sptep, sp);

	}



	for (;

	     shadow_walk_okay(&iterator) && iterator.level > hlevel;

	     shadow_walk_next(&iterator)) {

		gfn_t direct_gfn;



		level = iterator.level;

		sptep = iterator.sptep;



		validate_direct_spte(vcpu, sptep, direct_access);



		drop_large_spte(vcpu, sptep);



		if (is_shadow_present_pte(*sptep))

			continue;



		direct_gfn = gw->gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);



		sp = kvm_mmu_get_page(vcpu, direct_gfn, addr, level-1,

				      true, direct_access, sptep);

		link_shadow_page(sptep, sp);

	}



	sptep = iterator.sptep;

	level = iterator.level;



	mmu_set_spte(vcpu, sptep, access, gw->pte_access & access,

		     user_fault, write_fault, dirty, ptwrite, level,

		     gw->gfn, pfn, false, true);



	return sptep;



out_gpte_changed:

	kvm_mmu_put_page(sp, sptep);

	kvm_release_pfn_clean(pfn);

	return NULL;

}



/*

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