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KVM: MMU: Simplify calculation of pte access
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The nx bit is awkwardly placed in the 63rd bit position; furthermore it
has a reversed meaning compared to the other bits, which means we can't use
a bitwise and to calculate compounded access masks.

So, we simplify things by creating a new 3-bit exec/write/user access word,
and doing all calculations in that.

Signed-off-by: Avi Kivity <avi@qumranet.com>
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Avi Kivity committed Jan 30, 2008
1 parent b3e4e63 commit fe135d2
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Showing 2 changed files with 43 additions and 29 deletions.
14 changes: 10 additions & 4 deletions drivers/kvm/mmu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -85,7 +85,8 @@ static int dbg = 1;
#define PT_PAGE_SIZE_MASK (1ULL << 7)
#define PT_PAT_MASK (1ULL << 7)
#define PT_GLOBAL_MASK (1ULL << 8)
#define PT64_NX_MASK (1ULL << 63)
#define PT64_NX_SHIFT 63
#define PT64_NX_MASK (1ULL << PT64_NX_SHIFT)

#define PT_PAT_SHIFT 7
#define PT_DIR_PAT_SHIFT 12
Expand Down Expand Up @@ -153,6 +154,11 @@ static int dbg = 1;

#define RMAP_EXT 4

#define ACC_EXEC_MASK 1
#define ACC_WRITE_MASK PT_WRITABLE_MASK
#define ACC_USER_MASK PT_USER_MASK
#define ACC_ALL (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)

struct kvm_rmap_desc {
u64 *shadow_ptes[RMAP_EXT];
struct kvm_rmap_desc *more;
Expand Down Expand Up @@ -921,7 +927,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, struct page *page)
>> PAGE_SHIFT;
new_table = kvm_mmu_get_page(vcpu, pseudo_gfn,
v, level - 1,
1, 3, &table[index]);
1, ACC_ALL, &table[index]);
if (!new_table) {
pgprintk("nonpaging_map: ENOMEM\n");
kvm_release_page_clean(page);
Expand Down Expand Up @@ -988,7 +994,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)

ASSERT(!VALID_PAGE(root));
sp = kvm_mmu_get_page(vcpu, root_gfn, 0,
PT64_ROOT_LEVEL, 0, 0, NULL);
PT64_ROOT_LEVEL, 0, ACC_ALL, NULL);
root = __pa(sp->spt);
++sp->root_count;
vcpu->mmu.root_hpa = root;
Expand All @@ -1009,7 +1015,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
root_gfn = 0;
sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
PT32_ROOT_LEVEL, !is_paging(vcpu),
0, NULL);
ACC_ALL, NULL);
root = __pa(sp->spt);
++sp->root_count;
vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;
Expand Down
58 changes: 33 additions & 25 deletions drivers/kvm/paging_tmpl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -66,7 +66,8 @@ struct guest_walker {
int level;
gfn_t table_gfn[PT_MAX_FULL_LEVELS];
pt_element_t pte;
pt_element_t inherited_ar;
unsigned pt_access;
unsigned pte_access;
gfn_t gfn;
u32 error_code;
};
Expand Down Expand Up @@ -110,7 +111,7 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
{
pt_element_t pte;
gfn_t table_gfn;
unsigned index;
unsigned index, pt_access, pte_access;
gpa_t pte_gpa;

pgprintk("%s: addr %lx\n", __FUNCTION__, addr);
Expand All @@ -128,7 +129,7 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
ASSERT((!is_long_mode(vcpu) && is_pae(vcpu)) ||
(vcpu->cr3 & CR3_NONPAE_RESERVED_BITS) == 0);

walker->inherited_ar = PT_USER_MASK | PT_WRITABLE_MASK;
pt_access = ACC_ALL;

for (;;) {
index = PT_INDEX(addr, walker->level);
Expand Down Expand Up @@ -165,6 +166,14 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
pte |= PT_ACCESSED_MASK;
}

pte_access = pte & (PT_WRITABLE_MASK | PT_USER_MASK);
pte_access |= ACC_EXEC_MASK;
#if PTTYPE == 64
if (is_nx(vcpu))
pte_access &= ~(pte >> PT64_NX_SHIFT);
#endif
pte_access &= pt_access;

if (walker->level == PT_PAGE_TABLE_LEVEL) {
walker->gfn = gpte_to_gfn(pte);
break;
Expand All @@ -180,7 +189,7 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
break;
}

walker->inherited_ar &= pte;
pt_access = pte_access;
--walker->level;
}

Expand All @@ -197,7 +206,10 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
}

walker->pte = pte;
pgprintk("%s: pte %llx\n", __FUNCTION__, (u64)pte);
walker->pt_access = pt_access;
walker->pte_access = pte_access;
pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
__FUNCTION__, (u64)pte, pt_access, pte_access);
return 1;

not_present:
Expand All @@ -218,7 +230,8 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
}

static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
u64 *shadow_pte, u64 access_bits,
u64 *shadow_pte, unsigned pt_access,
unsigned pte_access,
int user_fault, int write_fault,
int *ptwrite, struct guest_walker *walker,
gfn_t gfn)
Expand All @@ -228,12 +241,11 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
int was_rmapped = is_rmap_pte(*shadow_pte);
struct page *page;

pgprintk("%s: spte %llx gpte %llx access %llx write_fault %d"
pgprintk("%s: spte %llx gpte %llx access %x write_fault %d"
" user_fault %d gfn %lx\n",
__FUNCTION__, *shadow_pte, (u64)gpte, access_bits,
__FUNCTION__, *shadow_pte, (u64)gpte, pt_access,
write_fault, user_fault, gfn);

access_bits &= gpte;
/*
* We don't set the accessed bit, since we sometimes want to see
* whether the guest actually used the pte (in order to detect
Expand All @@ -242,12 +254,12 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
spte = PT_PRESENT_MASK | PT_DIRTY_MASK;
spte |= gpte & PT64_NX_MASK;
if (!dirty)
access_bits &= ~PT_WRITABLE_MASK;
pte_access &= ~ACC_WRITE_MASK;

page = gfn_to_page(vcpu->kvm, gfn);

spte |= PT_PRESENT_MASK;
if (access_bits & PT_USER_MASK)
if (pte_access & ACC_USER_MASK)
spte |= PT_USER_MASK;

if (is_error_page(page)) {
Expand All @@ -259,7 +271,7 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,

spte |= page_to_phys(page);

if ((access_bits & PT_WRITABLE_MASK)
if ((pte_access & ACC_WRITE_MASK)
|| (write_fault && !is_write_protection(vcpu) && !user_fault)) {
struct kvm_mmu_page *shadow;

Expand All @@ -273,7 +285,7 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,
if (shadow) {
pgprintk("%s: found shadow page for %lx, marking ro\n",
__FUNCTION__, gfn);
access_bits &= ~PT_WRITABLE_MASK;
pte_access &= ~ACC_WRITE_MASK;
if (is_writeble_pte(spte)) {
spte &= ~PT_WRITABLE_MASK;
kvm_x86_ops->tlb_flush(vcpu);
Expand All @@ -285,7 +297,7 @@ static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,

unshadowed:

if (access_bits & PT_WRITABLE_MASK)
if (pte_access & ACC_WRITE_MASK)
mark_page_dirty(vcpu->kvm, gfn);

pgprintk("%s: setting spte %llx\n", __FUNCTION__, spte);
Expand Down Expand Up @@ -317,8 +329,8 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
if (bytes < sizeof(pt_element_t))
return;
pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);
FNAME(set_pte)(vcpu, gpte, spte, PT_USER_MASK | PT_WRITABLE_MASK, 0,
0, NULL, NULL, gpte_to_gfn(gpte));
FNAME(set_pte)(vcpu, gpte, spte, ACC_ALL, ACC_ALL,
0, 0, NULL, NULL, gpte_to_gfn(gpte));
}

/*
Expand All @@ -331,6 +343,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
hpa_t shadow_addr;
int level;
u64 *shadow_ent;
unsigned access = walker->pt_access;

if (!is_present_pte(walker->pte))
return NULL;
Expand All @@ -349,7 +362,6 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
u64 shadow_pte;
int metaphysical;
gfn_t table_gfn;
unsigned hugepage_access = 0;

shadow_ent = ((u64 *)__va(shadow_addr)) + index;
if (is_shadow_present_pte(*shadow_ent)) {
Expand All @@ -365,20 +377,15 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
if (level - 1 == PT_PAGE_TABLE_LEVEL
&& walker->level == PT_DIRECTORY_LEVEL) {
metaphysical = 1;
hugepage_access = walker->pte;
hugepage_access &= PT_USER_MASK | PT_WRITABLE_MASK;
if (!is_dirty_pte(walker->pte))
hugepage_access &= ~PT_WRITABLE_MASK;
hugepage_access >>= PT_WRITABLE_SHIFT;
if (walker->pte & PT64_NX_MASK)
hugepage_access |= (1 << 2);
access &= ~ACC_WRITE_MASK;
table_gfn = gpte_to_gfn(walker->pte);
} else {
metaphysical = 0;
table_gfn = walker->table_gfn[level - 2];
}
shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
metaphysical, hugepage_access,
metaphysical, access,
shadow_ent);
shadow_addr = __pa(shadow_page->spt);
shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK
Expand All @@ -387,7 +394,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
}

FNAME(set_pte)(vcpu, walker->pte, shadow_ent,
walker->inherited_ar, user_fault, write_fault,
access, walker->pte_access & access,
user_fault, write_fault,
ptwrite, walker, walker->gfn);

return shadow_ent;
Expand Down

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