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KVM: MMU: optimize to handle dirty bit
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If dirty bit is not set, we can make the pte access read-only to avoid handing
dirty bit everywhere

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
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Xiao Guangrong authored and Avi Kivity committed Jul 24, 2011
1 parent bebb106 commit 640d9b0
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Showing 2 changed files with 25 additions and 34 deletions.
13 changes: 6 additions & 7 deletions arch/x86/kvm/mmu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1923,7 +1923,7 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,

static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
unsigned pte_access, int user_fault,
int write_fault, int dirty, int level,
int write_fault, int level,
gfn_t gfn, pfn_t pfn, bool speculative,
bool can_unsync, bool host_writable)
{
Expand All @@ -1938,8 +1938,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
spte = PT_PRESENT_MASK;
if (!speculative)
spte |= shadow_accessed_mask;
if (!dirty)
pte_access &= ~ACC_WRITE_MASK;

if (pte_access & ACC_EXEC_MASK)
spte |= shadow_x_mask;
else
Expand Down Expand Up @@ -2023,7 +2022,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,

static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
unsigned pt_access, unsigned pte_access,
int user_fault, int write_fault, int dirty,
int user_fault, int write_fault,
int *ptwrite, int level, gfn_t gfn,
pfn_t pfn, bool speculative,
bool host_writable)
Expand Down Expand Up @@ -2059,7 +2058,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
}

if (set_spte(vcpu, sptep, pte_access, user_fault, write_fault,
dirty, level, gfn, pfn, speculative, true,
level, gfn, pfn, speculative, true,
host_writable)) {
if (write_fault)
*ptwrite = 1;
Expand Down Expand Up @@ -2129,7 +2128,7 @@ static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,

for (i = 0; i < ret; i++, gfn++, start++)
mmu_set_spte(vcpu, start, ACC_ALL,
access, 0, 0, 1, NULL,
access, 0, 0, NULL,
sp->role.level, gfn,
page_to_pfn(pages[i]), true, true);

Expand Down Expand Up @@ -2193,7 +2192,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
unsigned pte_access = ACC_ALL;

mmu_set_spte(vcpu, iterator.sptep, ACC_ALL, pte_access,
0, write, 1, &pt_write,
0, write, &pt_write,
level, gfn, pfn, prefault, map_writable);
direct_pte_prefetch(vcpu, iterator.sptep);
++vcpu->stat.pf_fixed;
Expand Down
46 changes: 19 additions & 27 deletions arch/x86/kvm/paging_tmpl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -101,11 +101,15 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
return (ret != orig_pte);
}

static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
bool last)
{
unsigned access;

access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
if (last && !is_dirty_gpte(gpte))
access &= ~ACC_WRITE_MASK;

#if PTTYPE == 64
if (vcpu->arch.mmu.nx)
access &= ~(gpte >> PT64_NX_SHIFT);
Expand Down Expand Up @@ -232,8 +236,6 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
pte |= PT_ACCESSED_MASK;
}

pte_access = pt_access & FNAME(gpte_access)(vcpu, pte);

walker->ptes[walker->level - 1] = pte;

if (FNAME(is_last_gpte)(walker, vcpu, mmu, pte)) {
Expand Down Expand Up @@ -268,7 +270,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
break;
}

pt_access = pte_access;
pt_access &= FNAME(gpte_access)(vcpu, pte, false);
--walker->level;
}

Expand All @@ -293,6 +295,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
walker->ptes[walker->level - 1] = pte;
}

pte_access = pt_access & FNAME(gpte_access)(vcpu, pte, true);
walker->pt_access = pt_access;
walker->pte_access = pte_access;
pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
Expand Down Expand Up @@ -367,7 +370,7 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
return;

pgprintk("%s: gpte %llx spte %p\n", __func__, (u64)gpte, spte);
pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte, true);
pfn = gfn_to_pfn_atomic(vcpu->kvm, gpte_to_gfn(gpte));
if (is_error_pfn(pfn)) {
kvm_release_pfn_clean(pfn);
Expand All @@ -379,7 +382,7 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
* vcpu->arch.update_pte.pfn was fetched from get_user_pages(write = 1).
*/
mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
is_dirty_gpte(gpte), NULL, PT_PAGE_TABLE_LEVEL,
NULL, PT_PAGE_TABLE_LEVEL,
gpte_to_gfn(gpte), pfn, true, true);
}

Expand Down Expand Up @@ -430,7 +433,6 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
unsigned pte_access;
gfn_t gfn;
pfn_t pfn;
bool dirty;

if (spte == sptep)
continue;
Expand All @@ -443,18 +445,18 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
if (FNAME(prefetch_invalid_gpte)(vcpu, sp, spte, gpte))
continue;

pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte,
true);
gfn = gpte_to_gfn(gpte);
dirty = is_dirty_gpte(gpte);
pfn = pte_prefetch_gfn_to_pfn(vcpu, gfn,
(pte_access & ACC_WRITE_MASK) && dirty);
pte_access & ACC_WRITE_MASK);
if (is_error_pfn(pfn)) {
kvm_release_pfn_clean(pfn);
break;
}

mmu_set_spte(vcpu, spte, sp->role.access, pte_access, 0, 0,
dirty, NULL, PT_PAGE_TABLE_LEVEL, gfn,
NULL, PT_PAGE_TABLE_LEVEL, gfn,
pfn, true, true);
}
}
Expand All @@ -470,7 +472,6 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
{
unsigned access = gw->pt_access;
struct kvm_mmu_page *sp = NULL;
bool dirty = is_dirty_gpte(gw->ptes[gw->level - 1]);
int top_level;
unsigned direct_access;
struct kvm_shadow_walk_iterator it;
Expand All @@ -479,8 +480,6 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
return NULL;

direct_access = gw->pt_access & gw->pte_access;
if (!dirty)
direct_access &= ~ACC_WRITE_MASK;

top_level = vcpu->arch.mmu.root_level;
if (top_level == PT32E_ROOT_LEVEL)
Expand Down Expand Up @@ -539,7 +538,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
}

mmu_set_spte(vcpu, it.sptep, access, gw->pte_access & access,
user_fault, write_fault, dirty, ptwrite, it.level,
user_fault, write_fault, ptwrite, it.level,
gw->gfn, pfn, prefault, map_writable);
FNAME(pte_prefetch)(vcpu, gw, it.sptep);

Expand Down Expand Up @@ -622,17 +621,9 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
return 0;

/* mmio */
if (is_error_pfn(pfn)) {
unsigned access = walker.pte_access;
bool dirty = is_dirty_gpte(walker.ptes[walker.level - 1]);

if (!dirty)
access &= ~ACC_WRITE_MASK;

if (is_error_pfn(pfn))
return kvm_handle_bad_page(vcpu, mmu_is_nested(vcpu) ? 0 :
addr, access, walker.gfn, pfn);
}

addr, walker.pte_access, walker.gfn, pfn);
spin_lock(&vcpu->kvm->mmu_lock);
if (mmu_notifier_retry(vcpu, mmu_seq))
goto out_unlock;
Expand Down Expand Up @@ -849,11 +840,12 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
}

nr_present++;
pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte,
true);
host_writable = sp->spt[i] & SPTE_HOST_WRITEABLE;

set_spte(vcpu, &sp->spt[i], pte_access, 0, 0,
is_dirty_gpte(gpte), PT_PAGE_TABLE_LEVEL, gfn,
PT_PAGE_TABLE_LEVEL, gfn,
spte_to_pfn(sp->spt[i]), true, false,
host_writable);
}
Expand Down

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