[PATCH 09/14] KVM: x86/mmu: Rely on host page tables to find HugeTLB mappings

Sean Christopherson
2020-01-08T20:27:42Z

Remove KVM's HugeTLB specific logic and instead rely on walking the host
page tables (already done for THP) to identify HugeTLB mappings.
Eliminating the HugeTLB-only logic avoids taking mmap_sem and calling
find_vma() for all hugepage compatible page faults, and simplifies KVM's
page fault code by consolidating all hugepage adjustments into a common
helper.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu/mmu.c | 84 ++++++++++------------------------
arch/x86/kvm/mmu/paging_tmpl.h | 15 +++---
2 files changed, 29 insertions(+), 70 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7d78d1d996ed..68aec984f953 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1286,23 +1286,6 @@ static bool mmu_gfn_lpage_is_disallowed(struct kvm_vcpu *vcpu, gfn_t gfn,
return __mmu_gfn_lpage_is_disallowed(gfn, level, slot);
}

-static int host_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn)
-{
- unsigned long page_size;
- int i, ret = 0;
-
- page_size = kvm_host_page_size(vcpu, gfn);
-
- for (i = PT_PAGE_TABLE_LEVEL; i <= PT_MAX_HUGEPAGE_LEVEL; ++i) {
- if (page_size >= KVM_HPAGE_SIZE(i))
- ret = i;
- else
- break;
- }
-
- return ret;
-}
-
static inline bool memslot_valid_for_gpte(struct kvm_memory_slot *slot,
bool no_dirty_log)
{
@@ -1327,43 +1310,25 @@ gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu, gfn_t gfn,
return slot;
}

-static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn,
- int *max_levelp)
+static int max_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn,
+ int max_level)
{
- int host_level, max_level = *max_levelp;
struct kvm_memory_slot *slot;

if (unlikely(max_level == PT_PAGE_TABLE_LEVEL))
return PT_PAGE_TABLE_LEVEL;

- slot = kvm_vcpu_gfn_to_memslot(vcpu, large_gfn);
- if (!memslot_valid_for_gpte(slot, true)) {
- *max_levelp = PT_PAGE_TABLE_LEVEL;
+ slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+ if (!memslot_valid_for_gpte(slot, true))
return PT_PAGE_TABLE_LEVEL;
- }

max_level = min(max_level, kvm_x86_ops->get_lpage_level());
for ( ; max_level > PT_PAGE_TABLE_LEVEL; max_level--) {
- if (!__mmu_gfn_lpage_is_disallowed(large_gfn, max_level, slot))
+ if (!__mmu_gfn_lpage_is_disallowed(gfn, max_level, slot))
break;
}

- *max_levelp = max_level;
-
- if (max_level == PT_PAGE_TABLE_LEVEL)
- return PT_PAGE_TABLE_LEVEL;
-
- /*
- * Note, host_mapping_level() does *not* handle transparent huge pages.
- * As suggested by "mapping", it reflects the page size established by
- * the associated vma, if there is one, i.e. host_mapping_level() will
- * return a huge page level if and only if a vma exists and the backing
- * implementation for the vma uses huge pages, e.g. hugetlbfs and dax.
- * So, do not propagate host_mapping_level() to max_level as KVM can
- * still promote the guest mapping to a huge page in the THP case.
- */
- host_level = host_mapping_level(vcpu, large_gfn);
- return min(host_level, max_level);
+ return max_level;
}

/*
@@ -3137,7 +3102,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,

/*
* Other vcpu creates new sp in the window between
- * mapping_level() and acquiring mmu-lock. We can
+ * max_mapping_level() and acquiring mmu-lock. We can
* allow guest to retry the access, the mapping can
* be fixed if guest refault.
*/
@@ -3364,24 +3329,23 @@ static int host_pfn_mapping_level(struct kvm_vcpu *vcpu, gfn_t gfn,
return level;
}

-static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
- int max_level, kvm_pfn_t *pfnp,
- int *levelp)
+static int kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
+ int max_level, kvm_pfn_t *pfnp)
{
kvm_pfn_t pfn = *pfnp;
- int level = *levelp;
kvm_pfn_t mask;
+ int level;

- if (max_level == PT_PAGE_TABLE_LEVEL || level > PT_PAGE_TABLE_LEVEL)
- return;
+ if (max_level == PT_PAGE_TABLE_LEVEL)
+ return PT_PAGE_TABLE_LEVEL;

if (is_error_noslot_pfn(pfn) || kvm_is_reserved_pfn(pfn) ||
kvm_is_zone_device_pfn(pfn))
- return;
+ return PT_PAGE_TABLE_LEVEL;

level = host_pfn_mapping_level(vcpu, gfn, pfn);
if (level == PT_PAGE_TABLE_LEVEL)
- return;
+ return level;

level = min(level, max_level);

@@ -3389,10 +3353,11 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, gfn_t gfn,
* mmu_notifier_retry() was successful and mmu_lock is held, so
* the pmd can't be split from under us.
*/
- *levelp = level;
mask = KVM_PAGES_PER_HPAGE(level) - 1;
VM_BUG_ON((gfn & mask) != (pfn & mask));
*pfnp = pfn & ~mask;
+
+ return level;
}

static void disallowed_hugepage_adjust(struct kvm_shadow_walk_iterator it,
@@ -3419,20 +3384,19 @@ static void disallowed_hugepage_adjust(struct kvm_shadow_walk_iterator it,
}

static int __direct_map(struct kvm_vcpu *vcpu, gpa_t gpa, int write,
- int map_writable, int level, int max_level,
- kvm_pfn_t pfn, bool prefault,
- bool account_disallowed_nx_lpage)
+ int map_writable, int max_level, kvm_pfn_t pfn,
+ bool prefault, bool account_disallowed_nx_lpage)
{
struct kvm_shadow_walk_iterator it;
struct kvm_mmu_page *sp;
- int ret;
+ int level, ret;
gfn_t gfn = gpa >> PAGE_SHIFT;
gfn_t base_gfn = gfn;

if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
return RET_PF_RETRY;

- transparent_hugepage_adjust(vcpu, gfn, max_level, &pfn, &level);
+ level = kvm_mmu_hugepage_adjust(vcpu, gfn, max_level, &pfn);

trace_kvm_mmu_spte_requested(gpa, level, pfn);
for_each_shadow_entry(vcpu, gpa, it) {
@@ -4206,7 +4170,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
gfn_t gfn = gpa >> PAGE_SHIFT;
unsigned long mmu_seq;
kvm_pfn_t pfn;
- int level, r;
+ int r;

if (page_fault_handle_page_track(vcpu, error_code, gfn))
return RET_PF_EMULATE;
@@ -4218,9 +4182,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
if (lpage_disallowed)
max_level = PT_PAGE_TABLE_LEVEL;

- level = mapping_level(vcpu, gfn, &max_level);
- if (level > PT_PAGE_TABLE_LEVEL)
- gfn &= ~(KVM_PAGES_PER_HPAGE(level) - 1);
+ max_level = max_mapping_level(vcpu, gfn, max_level);

if (fast_page_fault(vcpu, gpa, error_code))
return RET_PF_RETRY;
@@ -4240,7 +4202,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
goto out_unlock;
if (make_mmu_pages_available(vcpu) < 0)
goto out_unlock;
- r = __direct_map(vcpu, gpa, write, map_writable, level, max_level, pfn,
+ r = __direct_map(vcpu, gpa, write, map_writable, max_level, pfn,
prefault, is_tdp && lpage_disallowed);

out_unlock:
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 0029f7870865..841506a55815 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -613,14 +613,14 @@ static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
*/
static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
struct guest_walker *gw,
- int write_fault, int hlevel, int max_level,
+ int write_fault, int max_level,
kvm_pfn_t pfn, bool map_writable, bool prefault,
bool lpage_disallowed)
{
struct kvm_mmu_page *sp = NULL;
struct kvm_shadow_walk_iterator it;
unsigned direct_access, access = gw->pt_access;
- int top_level, ret;
+ int top_level, hlevel, ret;
gfn_t gfn, base_gfn;

direct_access = gw->pte_access;
@@ -673,7 +673,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
gfn = gw->gfn | ((addr & PT_LVL_OFFSET_MASK(gw->level)) >> PAGE_SHIFT);
base_gfn = gfn;

- transparent_hugepage_adjust(vcpu, gw->gfn, max_level, &pfn, &hlevel);
+ hlevel = kvm_mmu_hugepage_adjust(vcpu, gw->gfn, max_level, &pfn);

trace_kvm_mmu_spte_requested(addr, gw->level, pfn);

@@ -775,7 +775,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
struct guest_walker walker;
int r;
kvm_pfn_t pfn;
- int level;
unsigned long mmu_seq;
bool map_writable, is_self_change_mapping;
bool lpage_disallowed = (error_code & PFERR_FETCH_MASK) &&
@@ -825,9 +824,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
else
max_level = walker.level;

- level = mapping_level(vcpu, walker.gfn, &max_level);
- if (level > PT_PAGE_TABLE_LEVEL)
- walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
+ max_level = max_mapping_level(vcpu, walker.gfn, max_level);

mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
@@ -867,8 +864,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
if (make_mmu_pages_available(vcpu) < 0)
goto out_unlock;
- r = FNAME(fetch)(vcpu, addr, &walker, write_fault, level, max_level,
- pfn, map_writable, prefault, lpage_disallowed);
+ r = FNAME(fetch)(vcpu, addr, &walker, write_fault, max_level, pfn,
+ map_writable, prefault, lpage_disallowed);
kvm_mmu_audit(vcpu, AUDIT_POST_PAGE_FAULT);

out_unlock:
--
2.24.1