[PATCH v3 15/15] KVM: arm64: Handle stage-2 faults in parallel

Oliver Upton
2022-10-27T22:24:04Z

The stage-2 map walker has been made parallel-aware, and as such can be
called while only holding the read side of the MMU lock. Rip out the
conditional locking in user_mem_abort() and instead grab the read lock.
Continue to take the write lock from other callsites to
kvm_pgtable_stage2_map().

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/include/asm/kvm_pgtable.h | 3 ++-
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 2 +-
arch/arm64/kvm/hyp/pgtable.c | 5 +++--
arch/arm64/kvm/mmu.c | 31 ++++++---------------------
4 files changed, 13 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 7634b6964779..a874ce0ce7b5 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -412,6 +412,7 @@ void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pg
* @prot: Permissions and attributes for the mapping.
* @mc: Cache of pre-allocated and zeroed memory from which to allocate
* page-table pages.
+ * @flags: Flags to control the page-table walk (ex. a shared walk)
*
* The offset of @addr within a page is ignored, @size is rounded-up to
* the next page boundary and @phys is rounded-down to the previous page
@@ -433,7 +434,7 @@ void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pg
*/
int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
u64 phys, enum kvm_pgtable_prot prot,
- void *mc);
+ void *mc, enum kvm_pgtable_walk_flags flags);

/**
* kvm_pgtable_stage2_set_owner() - Unmap and annotate pages in the IPA space to
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 735769886b55..f6d82bf33ce1 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -257,7 +257,7 @@ static inline int __host_stage2_idmap(u64 start, u64 end,
enum kvm_pgtable_prot prot)
{
return kvm_pgtable_stage2_map(&host_kvm.pgt, start, end - start, start,
- prot, &host_s2_pool);
+ prot, &host_s2_pool, 0);
}

/*
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index d08e14008bfb..9ffe2e0bccb9 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -912,7 +912,7 @@ static int stage2_map_walker(const struct kvm_pgtable_visit_ctx *ctx,

int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
u64 phys, enum kvm_pgtable_prot prot,
- void *mc)
+ void *mc, enum kvm_pgtable_walk_flags flags)
{
int ret;
struct stage2_map_data map_data = {
@@ -923,7 +923,8 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
};
struct kvm_pgtable_walker walker = {
.cb = stage2_map_walker,
- .flags = KVM_PGTABLE_WALK_TABLE_PRE |
+ .flags = flags |
+ KVM_PGTABLE_WALK_TABLE_PRE |
KVM_PGTABLE_WALK_LEAF,
.arg = &map_data,
};
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a1a623c5b069..93f014a97abf 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -861,7 +861,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,

write_lock(&kvm->mmu_lock);
ret = kvm_pgtable_stage2_map(pgt, addr, PAGE_SIZE, pa, prot,
- &cache);
+ &cache, 0);
write_unlock(&kvm->mmu_lock);
if (ret)
break;
@@ -1156,7 +1156,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
gfn_t gfn;
kvm_pfn_t pfn;
bool logging_active = memslot_is_logging(memslot);
- bool use_read_lock = false;
unsigned long fault_level = kvm_vcpu_trap_get_fault_level(vcpu);
unsigned long vma_pagesize, fault_granule;
enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
@@ -1191,8 +1190,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (logging_active) {
force_pte = true;
vma_shift = PAGE_SHIFT;
- use_read_lock = (fault_status == FSC_PERM && write_fault &&
- fault_granule == PAGE_SIZE);
} else {
vma_shift = get_vma_page_shift(vma, hva);
}
@@ -1291,15 +1288,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (exec_fault && device)
return -ENOEXEC;

- /*
- * To reduce MMU contentions and enhance concurrency during dirty
- * logging dirty logging, only acquire read lock for permission
- * relaxation.
- */
- if (use_read_lock)
- read_lock(&kvm->mmu_lock);
- else
- write_lock(&kvm->mmu_lock);
+ read_lock(&kvm->mmu_lock);
pgt = vcpu->arch.hw_mmu->pgt;
if (mmu_invalidate_retry(kvm, mmu_seq))
goto out_unlock;
@@ -1343,15 +1332,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
* permissions only if vma_pagesize equals fault_granule. Otherwise,
* kvm_pgtable_stage2_map() should be called to change block size.
*/
- if (fault_status == FSC_PERM && vma_pagesize == fault_granule) {
+ if (fault_status == FSC_PERM && vma_pagesize == fault_granule)
ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
- } else {
- WARN_ONCE(use_read_lock, "Attempted stage-2 map outside of write lock\n");
-
+ else
ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
__pfn_to_phys(pfn), prot,
- memcache);
- }
+ memcache, KVM_PGTABLE_WALK_SHARED);

/* Mark the page dirty only if the fault is handled successfully */
if (writable && !ret) {
@@ -1360,10 +1346,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
}

out_unlock:
- if (use_read_lock)
- read_unlock(&kvm->mmu_lock);
- else
- write_unlock(&kvm->mmu_lock);
+ read_unlock(&kvm->mmu_lock);
kvm_set_pfn_accessed(pfn);
kvm_release_pfn_clean(pfn);
return ret != -EAGAIN ? ret : 0;
@@ -1569,7 +1552,7 @@ bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
*/
kvm_pgtable_stage2_map(kvm->arch.mmu.pgt, range->start << PAGE_SHIFT,
PAGE_SIZE, __pfn_to_phys(pfn),
- KVM_PGTABLE_PROT_R, NULL);
+ KVM_PGTABLE_PROT_R, NULL, 0);

return false;
}
--
2.38.1.273.g43a17bfeac-goog