Commit 1df9f2dc authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Avi Kivity
Browse files

KVM: MMU: introduce the rules to modify shadow page table 



Introduce some interfaces to modify spte as linux kernel does:
- mmu_spte_clear_track_bits, it set the spte from present to nonpresent, and
  track the stat bits(accessed/dirty) of spte
- mmu_spte_clear_no_track, the same as mmu_spte_clear_track_bits except
  tracking the stat bits
- mmu_spte_set, set spte from nonpresent to present
- mmu_spte_update, only update the stat bits

Now, it does not allowed to set spte from present to present, later, we can
drop the atomicly opration for X86_32 host, and it is the preparing work to
get spte on X86_32 host out of the mmu lock

Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent d7c55201

arch/x86/kvm/mmu.c

+69 −34
Original line number Diff line number Diff line
@@ -299,12 +299,30 @@ static bool spte_is_bit_cleared(u64 old_spte, u64 new_spte, u64 bit_mask) 
	return (old_spte & bit_mask) && !(new_spte & bit_mask);

}



static void update_spte(u64 *sptep, u64 new_spte)

/* Rules for using mmu_spte_set:

 * Set the sptep from nonpresent to present.

 * Note: the sptep being assigned *must* be either not present

 * or in a state where the hardware will not attempt to update

 * the spte.

 */

static void mmu_spte_set(u64 *sptep, u64 new_spte)

{

	WARN_ON(is_shadow_present_pte(*sptep));

	__set_spte(sptep, new_spte);

}



/* Rules for using mmu_spte_update:

 * Update the state bits, it means the mapped pfn is not changged.

 */

static void mmu_spte_update(u64 *sptep, u64 new_spte)

{

	u64 mask, old_spte = *sptep;



	WARN_ON(!is_rmap_spte(new_spte));



	if (!is_shadow_present_pte(old_spte))

		return mmu_spte_set(sptep, new_spte);



	new_spte |= old_spte & shadow_dirty_mask;



	mask = shadow_accessed_mask;
@@ -325,6 +343,42 @@ static void update_spte(u64 *sptep, u64 new_spte) 
		kvm_set_pfn_dirty(spte_to_pfn(old_spte));

}



/*

 * Rules for using mmu_spte_clear_track_bits:

 * It sets the sptep from present to nonpresent, and track the

 * state bits, it is used to clear the last level sptep.

 */

static int mmu_spte_clear_track_bits(u64 *sptep)

{

	pfn_t pfn;

	u64 old_spte = *sptep;



	if (!spte_has_volatile_bits(old_spte))

		__set_spte(sptep, 0ull);

	else

		old_spte = __xchg_spte(sptep, 0ull);



	if (!is_rmap_spte(old_spte))

		return 0;



	pfn = spte_to_pfn(old_spte);

	if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)

		kvm_set_pfn_accessed(pfn);

	if (!shadow_dirty_mask || (old_spte & shadow_dirty_mask))

		kvm_set_pfn_dirty(pfn);

	return 1;

}



/*

 * Rules for using mmu_spte_clear_no_track:

 * Directly clear spte without caring the state bits of sptep,

 * it is used to set the upper level spte.

 */

static void mmu_spte_clear_no_track(u64 *sptep)

{

	__set_spte(sptep, 0ull);

}



static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,

				  struct kmem_cache *base_cache, int min)

{
@@ -746,30 +800,9 @@ static void rmap_remove(struct kvm *kvm, u64 *spte) 
	pte_list_remove(spte, rmapp);

}



static int set_spte_track_bits(u64 *sptep, u64 new_spte)

{

	pfn_t pfn;

	u64 old_spte = *sptep;



	if (!spte_has_volatile_bits(old_spte))

		__set_spte(sptep, new_spte);

	else

		old_spte = __xchg_spte(sptep, new_spte);



	if (!is_rmap_spte(old_spte))

		return 0;



	pfn = spte_to_pfn(old_spte);

	if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)

		kvm_set_pfn_accessed(pfn);

	if (!shadow_dirty_mask || (old_spte & shadow_dirty_mask))

		kvm_set_pfn_dirty(pfn);

	return 1;

}



static void drop_spte(struct kvm *kvm, u64 *sptep)

{

	if (set_spte_track_bits(sptep, 0ull))

	if (mmu_spte_clear_track_bits(sptep))

		rmap_remove(kvm, sptep);

}
@@ -787,7 +820,7 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn) 
		BUG_ON(!(*spte & PT_PRESENT_MASK));

		rmap_printk("rmap_write_protect: spte %p %llx\n", spte, *spte);

		if (is_writable_pte(*spte)) {

			update_spte(spte, *spte & ~PT_WRITABLE_MASK);

			mmu_spte_update(spte, *spte & ~PT_WRITABLE_MASK);

			write_protected = 1;

		}

		spte = rmap_next(kvm, rmapp, spte);
@@ -856,7 +889,8 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp, 
			new_spte &= ~PT_WRITABLE_MASK;

			new_spte &= ~SPTE_HOST_WRITEABLE;

			new_spte &= ~shadow_accessed_mask;

			set_spte_track_bits(spte, new_spte);

			mmu_spte_clear_track_bits(spte);

			mmu_spte_set(spte, new_spte);

			spte = rmap_next(kvm, rmapp, spte);

		}

	}
@@ -1077,7 +1111,7 @@ static void drop_parent_pte(struct kvm_mmu_page *sp, 
			    u64 *parent_pte)

{

	mmu_page_remove_parent_pte(sp, parent_pte);

	__set_spte(parent_pte, 0ull);

	mmu_spte_clear_no_track(parent_pte);

}



static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
@@ -1525,7 +1559,7 @@ static void link_shadow_page(u64 *sptep, struct kvm_mmu_page *sp) 
	spte = __pa(sp->spt)

		| PT_PRESENT_MASK | PT_ACCESSED_MASK

		| PT_WRITABLE_MASK | PT_USER_MASK;

	__set_spte(sptep, spte);

	mmu_spte_set(sptep, spte);

}



static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
@@ -1992,7 +2026,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, 
		mark_page_dirty(vcpu->kvm, gfn);



set_pte:

	update_spte(sptep, spte);

	mmu_spte_update(sptep, spte);

	/*

	 * If we overwrite a writable spte with a read-only one we

	 * should flush remote TLBs. Otherwise rmap_write_protect
@@ -2198,7 +2232,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write, 
				return -ENOMEM;

			}



			__set_spte(iterator.sptep,

			mmu_spte_set(iterator.sptep,

				     __pa(sp->spt)

				     | PT_PRESENT_MASK | PT_WRITABLE_MASK

				     | shadow_user_mask | shadow_x_mask
@@ -3439,7 +3473,8 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) 


			/* avoid RMW */

			if (is_writable_pte(pt[i]))

				update_spte(&pt[i], pt[i] & ~PT_WRITABLE_MASK);

				mmu_spte_update(&pt[i],

						pt[i] & ~PT_WRITABLE_MASK);

		}

	}

	kvm_flush_remote_tlbs(kvm);

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