[PATCH v4 10/18] KVM: MMU: remove bypass_guest_pf

From: Xiao Guangrong
Date: Mon Jul 11 2011 - 15:26:13 EST

The idea is from Avi:
| Maybe it's time to kill off bypass_guest_pf=1. It's not as effective as
| it used to be, since unsync pages always use shadow_trap_nonpresent_pte,
| and since we convert between the two nonpresent_ptes during sync and unsync.

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
---
Documentation/kernel-parameters.txt | 4 --
arch/x86/include/asm/kvm_host.h | 3 -
arch/x86/kvm/mmu.c | 83 ++++++++++-------------------------
arch/x86/kvm/mmu_audit.c | 12 -----
arch/x86/kvm/paging_tmpl.h | 51 +++------------------
arch/x86/kvm/vmx.c | 11 +----
arch/x86/kvm/x86.c | 1 -
7 files changed, 33 insertions(+), 132 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fd248a31..a06e4f1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1159,10 +1159,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
for all guests.
Default is 1 (enabled) if in 64bit or 32bit-PAE mode

- kvm-intel.bypass_guest_pf=
- [KVM,Intel] Disables bypassing of guest page faults
- on Intel chips. Default is 1 (enabled)
-
kvm-intel.ept= [KVM,Intel] Disable extended page tables
(virtualized MMU) support on capable Intel chips.
Default is 1 (enabled)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7b0834a..42e577d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -266,8 +266,6 @@ struct kvm_mmu {
gpa_t (*gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t gva, u32 access,
struct x86_exception *exception);
gpa_t (*translate_gpa)(struct kvm_vcpu *vcpu, gpa_t gpa, u32 access);
- void (*prefetch_page)(struct kvm_vcpu *vcpu,
- struct kvm_mmu_page *page);
int (*sync_page)(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp);
void (*invlpg)(struct kvm_vcpu *vcpu, gva_t gva);
@@ -638,7 +636,6 @@ void kvm_mmu_module_exit(void);
void kvm_mmu_destroy(struct kvm_vcpu *vcpu);
int kvm_mmu_create(struct kvm_vcpu *vcpu);
int kvm_mmu_setup(struct kvm_vcpu *vcpu);
-void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte);
void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
u64 dirty_mask, u64 nx_mask, u64 x_mask);

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2f8543c..5334b4e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -186,8 +186,6 @@ static struct kmem_cache *pte_list_desc_cache;
static struct kmem_cache *mmu_page_header_cache;
static struct percpu_counter kvm_total_used_mmu_pages;

-static u64 __read_mostly shadow_trap_nonpresent_pte;
-static u64 __read_mostly shadow_notrap_nonpresent_pte;
static u64 __read_mostly shadow_nx_mask;
static u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
static u64 __read_mostly shadow_user_mask;
@@ -199,13 +197,6 @@ static inline u64 rsvd_bits(int s, int e)
return ((1ULL << (e - s + 1)) - 1) << s;
}

-void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte)
-{
- shadow_trap_nonpresent_pte = trap_pte;
- shadow_notrap_nonpresent_pte = notrap_pte;
-}
-EXPORT_SYMBOL_GPL(kvm_mmu_set_nonpresent_ptes);
-
void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
u64 dirty_mask, u64 nx_mask, u64 x_mask)
{
@@ -229,8 +220,7 @@ static int is_nx(struct kvm_vcpu *vcpu)

static int is_shadow_present_pte(u64 pte)
{
- return pte != shadow_trap_nonpresent_pte
- && pte != shadow_notrap_nonpresent_pte;
+ return pte & PT_PRESENT_MASK;
}

static int is_large_pte(u64 pte)
@@ -777,9 +767,9 @@ static int set_spte_track_bits(u64 *sptep, u64 new_spte)
return 1;
}

-static void drop_spte(struct kvm *kvm, u64 *sptep, u64 new_spte)
+static void drop_spte(struct kvm *kvm, u64 *sptep)
{
- if (set_spte_track_bits(sptep, new_spte))
+ if (set_spte_track_bits(sptep, 0ull))
rmap_remove(kvm, sptep);
}

@@ -814,8 +804,7 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn)
BUG_ON((*spte & (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK)) != (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK));
pgprintk("rmap_write_protect(large): spte %p %llx %lld\n", spte, *spte, gfn);
if (is_writable_pte(*spte)) {
- drop_spte(kvm, spte,
- shadow_trap_nonpresent_pte);
+ drop_spte(kvm, spte);
--kvm->stat.lpages;
spte = NULL;
write_protected = 1;
@@ -836,7 +825,7 @@ static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,
while ((spte = rmap_next(kvm, rmapp, NULL))) {
BUG_ON(!(*spte & PT_PRESENT_MASK));
rmap_printk("kvm_rmap_unmap_hva: spte %p %llx\n", spte, *spte);
- drop_spte(kvm, spte, shadow_trap_nonpresent_pte);
+ drop_spte(kvm, spte);
need_tlb_flush = 1;
}
return need_tlb_flush;
@@ -858,7 +847,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
rmap_printk("kvm_set_pte_rmapp: spte %p %llx\n", spte, *spte);
need_flush = 1;
if (pte_write(*ptep)) {
- drop_spte(kvm, spte, shadow_trap_nonpresent_pte);
+ drop_spte(kvm, spte);
spte = rmap_next(kvm, rmapp, NULL);
} else {
new_spte = *spte &~ (PT64_BASE_ADDR_MASK);
@@ -1088,7 +1077,7 @@ 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, shadow_trap_nonpresent_pte);
+ __set_spte(parent_pte, 0ull);
}

static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
@@ -1130,15 +1119,6 @@ static void mark_unsync(u64 *spte)
kvm_mmu_mark_parents_unsync(sp);
}

-static void nonpaging_prefetch_page(struct kvm_vcpu *vcpu,
- struct kvm_mmu_page *sp)
-{
- int i;
-
- for (i = 0; i < PT64_ENT_PER_PAGE; ++i)
- sp->spt[i] = shadow_trap_nonpresent_pte;
-}
-
static int nonpaging_sync_page(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp)
{
@@ -1420,6 +1400,14 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
}
}

+static void init_shadow_page_table(struct kvm_mmu_page *sp)
+{
+ int i;
+
+ for (i = 0; i < PT64_ENT_PER_PAGE; ++i)
+ sp->spt[i] = 0ull;
+}
+
static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
gfn_t gfn,
gva_t gaddr,
@@ -1482,10 +1470,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,

account_shadowed(vcpu->kvm, gfn);
}
- if (shadow_trap_nonpresent_pte != shadow_notrap_nonpresent_pte)
- vcpu->arch.mmu.prefetch_page(vcpu, sp);
- else
- nonpaging_prefetch_page(vcpu, sp);
+ init_shadow_page_table(sp);
trace_kvm_mmu_get_page(sp, true);
return sp;
}
@@ -1546,7 +1531,7 @@ static void link_shadow_page(u64 *sptep, struct kvm_mmu_page *sp)
static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
{
if (is_large_pte(*sptep)) {
- drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
+ drop_spte(vcpu->kvm, sptep);
kvm_flush_remote_tlbs(vcpu->kvm);
}
}
@@ -1582,13 +1567,13 @@ static void mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
pte = *spte;
if (is_shadow_present_pte(pte)) {
if (is_last_spte(pte, sp->role.level))
- drop_spte(kvm, spte, shadow_trap_nonpresent_pte);
+ drop_spte(kvm, spte);
else {
child = page_header(pte & PT64_BASE_ADDR_MASK);
drop_parent_pte(child, spte);
}
}
- __set_spte(spte, shadow_trap_nonpresent_pte);
+
if (is_large_pte(pte))
--kvm->stat.lpages;
}
@@ -1769,20 +1754,6 @@ static void page_header_update_slot(struct kvm *kvm, void *pte, gfn_t gfn)
__set_bit(slot, sp->slot_bitmap);
}

-static void mmu_convert_notrap(struct kvm_mmu_page *sp)
-{
- int i;
- u64 *pt = sp->spt;
-
- if (shadow_trap_nonpresent_pte == shadow_notrap_nonpresent_pte)
- return;
-
- for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
- if (pt[i] == shadow_notrap_nonpresent_pte)
- __set_spte(&pt[i], shadow_trap_nonpresent_pte);
- }
-}
-
/*
* The function is based on mtrr_type_lookup() in
* arch/x86/kernel/cpu/mtrr/generic.c
@@ -1895,7 +1866,6 @@ static void __kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
sp->unsync = 1;

kvm_mmu_mark_parents_unsync(sp);
- mmu_convert_notrap(sp);
}

static void kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn)
@@ -1980,7 +1950,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
if (level > PT_PAGE_TABLE_LEVEL &&
has_wrprotected_page(vcpu->kvm, gfn, level)) {
ret = 1;
- drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
+ drop_spte(vcpu->kvm, sptep);
goto done;
}

@@ -2066,7 +2036,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
} else if (pfn != spte_to_pfn(*sptep)) {
pgprintk("hfn old %llx new %llx\n",
spte_to_pfn(*sptep), pfn);
- drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
+ drop_spte(vcpu->kvm, sptep);
kvm_flush_remote_tlbs(vcpu->kvm);
} else
was_rmapped = 1;
@@ -2162,7 +2132,7 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
spte = sp->spt + i;

for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
- if (*spte != shadow_trap_nonpresent_pte || spte == sptep) {
+ if (is_shadow_present_pte(*spte) || spte == sptep) {
if (!start)
continue;
if (direct_pte_prefetch_many(vcpu, sp, start, spte) < 0)
@@ -2214,7 +2184,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
break;
}

- if (*iterator.sptep == shadow_trap_nonpresent_pte) {
+ if (!is_shadow_present_pte(*iterator.sptep)) {
u64 base_addr = iterator.addr;

base_addr &= PT64_LVL_ADDR_MASK(iterator.level);
@@ -2748,7 +2718,6 @@ static int nonpaging_init_context(struct kvm_vcpu *vcpu,
context->page_fault = nonpaging_page_fault;
context->gva_to_gpa = nonpaging_gva_to_gpa;
context->free = nonpaging_free;
- context->prefetch_page = nonpaging_prefetch_page;
context->sync_page = nonpaging_sync_page;
context->invlpg = nonpaging_invlpg;
context->update_pte = nonpaging_update_pte;
@@ -2878,7 +2847,6 @@ static int paging64_init_context_common(struct kvm_vcpu *vcpu,
context->new_cr3 = paging_new_cr3;
context->page_fault = paging64_page_fault;
context->gva_to_gpa = paging64_gva_to_gpa;
- context->prefetch_page = paging64_prefetch_page;
context->sync_page = paging64_sync_page;
context->invlpg = paging64_invlpg;
context->update_pte = paging64_update_pte;
@@ -2907,7 +2875,6 @@ static int paging32_init_context(struct kvm_vcpu *vcpu,
context->page_fault = paging32_page_fault;
context->gva_to_gpa = paging32_gva_to_gpa;
context->free = paging_free;
- context->prefetch_page = paging32_prefetch_page;
context->sync_page = paging32_sync_page;
context->invlpg = paging32_invlpg;
context->update_pte = paging32_update_pte;
@@ -2932,7 +2899,6 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
context->new_cr3 = nonpaging_new_cr3;
context->page_fault = tdp_page_fault;
context->free = nonpaging_free;
- context->prefetch_page = nonpaging_prefetch_page;
context->sync_page = nonpaging_sync_page;
context->invlpg = nonpaging_invlpg;
context->update_pte = nonpaging_update_pte;
@@ -3443,8 +3409,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
continue;

if (is_large_pte(pt[i])) {
- drop_spte(kvm, &pt[i],
- shadow_trap_nonpresent_pte);
+ drop_spte(kvm, &pt[i]);
--kvm->stat.lpages;
continue;
}
diff --git a/arch/x86/kvm/mmu_audit.c b/arch/x86/kvm/mmu_audit.c
index 5f6223b..2460a26 100644
--- a/arch/x86/kvm/mmu_audit.c
+++ b/arch/x86/kvm/mmu_audit.c
@@ -99,18 +99,6 @@ static void audit_mappings(struct kvm_vcpu *vcpu, u64 *sptep, int level)
"level = %d\n", sp, level);
return;
}
-
- if (*sptep == shadow_notrap_nonpresent_pte) {
- audit_printk(vcpu->kvm, "notrap spte in unsync "
- "sp: %p\n", sp);
- return;
- }
- }
-
- if (sp->role.direct && *sptep == shadow_notrap_nonpresent_pte) {
- audit_printk(vcpu->kvm, "notrap spte in direct sp: %p\n",
- sp);
- return;
}

if (!is_shadow_present_pte(*sptep) || !is_last_spte(*sptep, level))
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index fa3b54b..a4565df 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -337,16 +337,11 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp, u64 *spte,
pt_element_t gpte)
{
- u64 nonpresent = shadow_trap_nonpresent_pte;
-
if (is_rsvd_bits_set(&vcpu->arch.mmu, gpte, PT_PAGE_TABLE_LEVEL))
goto no_present;

- if (!is_present_gpte(gpte)) {
- if (!sp->unsync)
- nonpresent = shadow_notrap_nonpresent_pte;
+ if (!is_present_gpte(gpte))
goto no_present;
- }

if (!(gpte & PT_ACCESSED_MASK))
goto no_present;
@@ -354,7 +349,7 @@ static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
return false;

no_present:
- drop_spte(vcpu->kvm, spte, nonpresent);
+ drop_spte(vcpu->kvm, spte);
return true;
}

@@ -437,7 +432,7 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
if (spte == sptep)
continue;

- if (*spte != shadow_trap_nonpresent_pte)
+ if (is_shadow_present_pte(*spte))
continue;

gpte = gptep[i];
@@ -687,11 +682,10 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
if (is_shadow_present_pte(*sptep)) {
if (is_large_pte(*sptep))
--vcpu->kvm->stat.lpages;
- drop_spte(vcpu->kvm, sptep,
- shadow_trap_nonpresent_pte);
+ drop_spte(vcpu->kvm, sptep);
need_flush = 1;
- } else
- __set_spte(sptep, shadow_trap_nonpresent_pte);
+ }
+
break;
}

@@ -751,36 +745,6 @@ static gpa_t FNAME(gva_to_gpa_nested)(struct kvm_vcpu *vcpu, gva_t vaddr,
return gpa;
}

-static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
- struct kvm_mmu_page *sp)
-{
- int i, j, offset, r;
- pt_element_t pt[256 / sizeof(pt_element_t)];
- gpa_t pte_gpa;
-
- if (sp->role.direct
- || (PTTYPE == 32 && sp->role.level > PT_PAGE_TABLE_LEVEL)) {
- nonpaging_prefetch_page(vcpu, sp);
- return;
- }
-
- pte_gpa = gfn_to_gpa(sp->gfn);
- if (PTTYPE == 32) {
- offset = sp->role.quadrant << PT64_LEVEL_BITS;
- pte_gpa += offset * sizeof(pt_element_t);
- }
-
- for (i = 0; i < PT64_ENT_PER_PAGE; i += ARRAY_SIZE(pt)) {
- r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa, pt, sizeof pt);
- pte_gpa += ARRAY_SIZE(pt) * sizeof(pt_element_t);
- for (j = 0; j < ARRAY_SIZE(pt); ++j)
- if (r || is_present_gpte(pt[j]))
- sp->spt[i+j] = shadow_trap_nonpresent_pte;
- else
- sp->spt[i+j] = shadow_notrap_nonpresent_pte;
- }
-}
-
/*
* Using the cached information from sp->gfns is safe because:
* - The spte has a reference to the struct page, so the pfn for a given gfn
@@ -833,8 +797,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
}

if (gfn != sp->gfns[i]) {
- drop_spte(vcpu->kvm, &sp->spt[i],
- shadow_trap_nonpresent_pte);
+ drop_spte(vcpu->kvm, &sp->spt[i]);
vcpu->kvm->tlbs_dirty++;
continue;
}
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f5b49c7..a644acb 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -49,9 +49,6 @@
MODULE_AUTHOR("Qumranet");
MODULE_LICENSE("GPL");

-static int __read_mostly bypass_guest_pf = 1;
-module_param(bypass_guest_pf, bool, S_IRUGO);
-
static int __read_mostly enable_vpid = 1;
module_param_named(vpid, enable_vpid, bool, 0444);

@@ -3632,8 +3629,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmcs_write32(PLE_WINDOW, ple_window);
}

- vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, !!bypass_guest_pf);
- vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, !!bypass_guest_pf);
+ vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, 0);
+ vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, 0);
vmcs_write32(CR3_TARGET_COUNT, 0); /* 22.2.1 */

vmcs_write16(HOST_FS_SELECTOR, 0); /* 22.2.4 */
@@ -7103,16 +7100,12 @@ static int __init vmx_init(void)
vmx_disable_intercept_for_msr(MSR_IA32_SYSENTER_EIP, false);

if (enable_ept) {
- bypass_guest_pf = 0;
kvm_mmu_set_mask_ptes(0ull, 0ull, 0ull, 0ull,
VMX_EPT_EXECUTABLE_MASK);
kvm_enable_tdp();
} else
kvm_disable_tdp();

- if (bypass_guest_pf)
- kvm_mmu_set_nonpresent_ptes(~0xffeull, 0ull);
-
return 0;

out3:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b3716f1..1811f0c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5025,7 +5025,6 @@ int kvm_arch_init(void *opaque)
kvm_init_msr_list();

kvm_x86_ops = ops;
- kvm_mmu_set_nonpresent_ptes(0ull, 0ull);
kvm_mmu_set_mask_ptes(PT_USER_MASK, PT_ACCESSED_MASK,
PT_DIRTY_MASK, PT64_NX_MASK, 0);

--
1.7.5.4

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