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KVM: x86/mmu: fast_page_fault support for the TDP MMU

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Make fast_page_fault interoperate with the TDP MMU by leveraging
walk_shadow_page_lockless_{begin,end} to acquire the RCU read lock and
introducing a new helper function kvm_tdp_mmu_fast_pf_get_last_sptep to
grab the lowest level sptep.

Suggested-by: Ben Gardon <bgardon@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210713220957.3493520-5-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack
2021-07-13 22:09:55 +00:00
committed by Paolo Bonzini
parent c5c8c7c530
commit 6e8eb2060c
3 changed files with 80 additions and 13 deletions
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50
arch/x86/kvm/mmu/mmu.c
View File

@@ -3108,15 +3108,41 @@ static bool is_access_allowed(u32 fault_err_code, u64 spte)
return spte & PT_PRESENT_MASK;
}
/*
* Returns the last level spte pointer of the shadow page walk for the given
* gpa, and sets *spte to the spte value. This spte may be non-preset. If no
* walk could be performed, returns NULL and *spte does not contain valid data.
*
* Contract:
* - Must be called between walk_shadow_page_lockless_{begin,end}.
* - The returned sptep must not be used after walk_shadow_page_lockless_end.
*/
static u64 *fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, gpa_t gpa, u64 *spte)
{
struct kvm_shadow_walk_iterator iterator;
u64 old_spte;
u64 *sptep = NULL;
for_each_shadow_entry_lockless(vcpu, gpa, iterator, old_spte) {
sptep = iterator.sptep;
*spte = old_spte;
if (!is_shadow_present_pte(old_spte))
break;
}
return sptep;
}
/*
* Returns one of RET_PF_INVALID, RET_PF_FIXED or RET_PF_SPURIOUS.
*/
static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
{
struct kvm_shadow_walk_iterator iterator;
struct kvm_mmu_page *sp;
int ret = RET_PF_INVALID;
u64 spte = 0ull;
u64 *sptep = NULL;
uint retry_count = 0;
if (!page_fault_can_be_fast(error_code))
@@ -3127,14 +3153,15 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
do {
u64 new_spte;
for_each_shadow_entry_lockless(vcpu, gpa, iterator, spte)
if (!is_shadow_present_pte(spte))
break;
if (is_tdp_mmu(vcpu->arch.mmu))
sptep = kvm_tdp_mmu_fast_pf_get_last_sptep(vcpu, gpa, &spte);
else
sptep = fast_pf_get_last_sptep(vcpu, gpa, &spte);
if (!is_shadow_present_pte(spte))
break;
sp = sptep_to_sp(iterator.sptep);
sp = sptep_to_sp(sptep);
if (!is_last_spte(spte, sp->role.level))
break;
@@ -3192,8 +3219,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
* since the gfn is not stable for indirect shadow page. See
* Documentation/virt/kvm/locking.rst to get more detail.
*/
if (fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte,
new_spte)) {
if (fast_pf_fix_direct_spte(vcpu, sp, sptep, spte, new_spte)) {
ret = RET_PF_FIXED;
break;
}
@@ -3206,7 +3232,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
} while (true);
trace_fast_page_fault(vcpu, gpa, error_code, iterator.sptep, spte, ret);
trace_fast_page_fault(vcpu, gpa, error_code, sptep, spte, ret);
walk_shadow_page_lockless_end(vcpu);
return ret;
@@ -3841,11 +3867,9 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
if (page_fault_handle_page_track(vcpu, error_code, gfn))
return RET_PF_EMULATE;
if (!is_tdp_mmu_fault) {
r = fast_page_fault(vcpu, gpa, error_code);
if (r != RET_PF_INVALID)
return r;
}
r = fast_page_fault(vcpu, gpa, error_code);
if (r != RET_PF_INVALID)
return r;
r = mmu_topup_memory_caches(vcpu, false);
if (r)

41
arch/x86/kvm/mmu/tdp_mmu.c
View File

@@ -527,6 +527,10 @@ static inline bool tdp_mmu_set_spte_atomic_no_dirty_log(struct kvm *kvm,
if (is_removed_spte(iter->old_spte))
return false;
/*
* Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and
* does not hold the mmu_lock.
*/
if (cmpxchg64(rcu_dereference(iter->sptep), iter->old_spte,
new_spte) != iter->old_spte)
return false;
@@ -1536,3 +1540,40 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
return leaf;
}
/*
* Returns the last level spte pointer of the shadow page walk for the given
* gpa, and sets *spte to the spte value. This spte may be non-preset. If no
* walk could be performed, returns NULL and *spte does not contain valid data.
*
* Contract:
* - Must be called between kvm_tdp_mmu_walk_lockless_{begin,end}.
* - The returned sptep must not be used after kvm_tdp_mmu_walk_lockless_end.
*
* WARNING: This function is only intended to be called during fast_page_fault.
*/
u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr,
u64 *spte)
{
struct tdp_iter iter;
struct kvm_mmu *mmu = vcpu->arch.mmu;
gfn_t gfn = addr >> PAGE_SHIFT;
tdp_ptep_t sptep = NULL;
tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) {
*spte = iter.old_spte;
sptep = iter.sptep;
}
/*
* Perform the rcu_dereference to get the raw spte pointer value since
* we are passing it up to fast_page_fault, which is shared with the
* legacy MMU and thus does not retain the TDP MMU-specific __rcu
* annotation.
*
* This is safe since fast_page_fault obeys the contracts of this
* function as well as all TDP MMU contracts around modifying SPTEs
* outside of mmu_lock.
*/
return rcu_dereference(sptep);
}

2
arch/x86/kvm/mmu/tdp_mmu.h
View File

@@ -89,6 +89,8 @@ static inline void kvm_tdp_mmu_walk_lockless_end(void)
int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
int *root_level);
u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr,
u64 *spte);
#ifdef CONFIG_X86_64
bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);