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kvm: x86: mmu: Refactor accessed/dirty checks in mmu_spte_update/clear

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This simplifies mmu_spte_update() a little bit.
The checks for clearing of accessed and dirty bits are refactored into
separate functions, which are used inside both mmu_spte_update() and
mmu_spte_clear_track_bits(), as well as kvm_test_age_rmapp(). The new
helper functions handle both the case when A/D bits are supported in
hardware and the case when they are not.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Junaid Shahid 2016-12-06 16:46:13 -08:00 committed by Radim Krčmář
parent 97dceba29a
commit 83ef6c8155
1 changed files with 32 additions and 36 deletions
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68
arch/x86/kvm/mmu.c
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@ -504,14 +504,16 @@ static bool spte_has_volatile_bits(u64 spte)
return true;
}
static bool spte_is_bit_cleared(u64 old_spte, u64 new_spte, u64 bit_mask)
static bool is_accessed_spte(u64 spte)
{
return (old_spte & bit_mask) && !(new_spte & bit_mask);
return shadow_accessed_mask ? spte & shadow_accessed_mask
: true;
}
static bool spte_is_bit_changed(u64 old_spte, u64 new_spte, u64 bit_mask)
static bool is_dirty_spte(u64 spte)
{
return (old_spte & bit_mask) != (new_spte & bit_mask);
return shadow_dirty_mask ? spte & shadow_dirty_mask
: spte & PT_WRITABLE_MASK;
}
/* Rules for using mmu_spte_set:
@ -534,17 +536,19 @@ static void mmu_spte_set(u64 *sptep, u64 new_spte)
* will find a read-only spte, even though the writable spte
* might be cached on a CPU's TLB, the return value indicates this
* case.
*
* Returns true if the TLB needs to be flushed
*/
static bool mmu_spte_update(u64 *sptep, u64 new_spte)
{
u64 old_spte = *sptep;
bool ret = false;
bool flush = false;
WARN_ON(!is_shadow_present_pte(new_spte));
if (!is_shadow_present_pte(old_spte)) {
mmu_spte_set(sptep, new_spte);
return ret;
return flush;
}
if (!spte_has_volatile_bits(old_spte))
@ -552,6 +556,8 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
else
old_spte = __update_clear_spte_slow(sptep, new_spte);
WARN_ON(spte_to_pfn(old_spte) != spte_to_pfn(new_spte));
/*
* For the spte updated out of mmu-lock is safe, since
* we always atomically update it, see the comments in
@ -559,38 +565,31 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
*/
if (spte_can_locklessly_be_made_writable(old_spte) &&
!is_writable_pte(new_spte))
ret = true;
if (!shadow_accessed_mask) {
/*
* We don't set page dirty when dropping non-writable spte.
* So do it now if the new spte is becoming non-writable.
*/
if (ret)
kvm_set_pfn_dirty(spte_to_pfn(old_spte));
return ret;
}
flush = true;
/*
* Flush TLB when accessed/dirty bits are changed in the page tables,
* Flush TLB when accessed/dirty states are changed in the page tables,
* to guarantee consistency between TLB and page tables.
*/
if (spte_is_bit_changed(old_spte, new_spte,
shadow_accessed_mask | shadow_dirty_mask))
ret = true;
if (spte_is_bit_cleared(old_spte, new_spte, shadow_accessed_mask))
if (is_accessed_spte(old_spte) && !is_accessed_spte(new_spte)) {
flush = true;
kvm_set_pfn_accessed(spte_to_pfn(old_spte));
if (spte_is_bit_cleared(old_spte, new_spte, shadow_dirty_mask))
kvm_set_pfn_dirty(spte_to_pfn(old_spte));
}
return ret;
if (is_dirty_spte(old_spte) && !is_dirty_spte(new_spte)) {
flush = true;
kvm_set_pfn_dirty(spte_to_pfn(old_spte));
}
return flush;
}
/*
* 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.
* Returns non-zero if the PTE was previously valid.
*/
static int mmu_spte_clear_track_bits(u64 *sptep)
{
@ -614,11 +613,12 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
*/
WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)
if (is_accessed_spte(old_spte))
kvm_set_pfn_accessed(pfn);
if (old_spte & (shadow_dirty_mask ? shadow_dirty_mask :
PT_WRITABLE_MASK))
if (is_dirty_spte(old_spte))
kvm_set_pfn_dirty(pfn);
return 1;
}
@ -1616,7 +1616,6 @@ static int kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
{
u64 *sptep;
struct rmap_iterator iter;
int young = 0;
/*
* If there's no access bit in the secondary pte set by the
@ -1626,14 +1625,11 @@ static int kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
if (!shadow_accessed_mask)
goto out;
for_each_rmap_spte(rmap_head, &iter, sptep) {
if (*sptep & shadow_accessed_mask) {
young = 1;
break;
}
}
for_each_rmap_spte(rmap_head, &iter, sptep)
if (is_accessed_spte(*sptep))
return 1;
out:
return young;
return 0;
}
#define RMAP_RECYCLE_THRESHOLD 1000