With a guest translation fault, we don't really need the memcache pages
when only installing a new entry to the existing page table or replacing
the table entry with a block entry. And with a guest permission fault,
we also don't need the memcache pages for a write_fault in dirty-logging
time if VMs are not configured with huge mappings.
The cases where allocations from memcache are required can be much more
precisely distinguished by comparing fault_granule and vma_pagesize.
Signed-off-by: Yanan Wang <wangyanan55@xxxxxxxxxx>
---
arch/arm64/kvm/mmu.c | 25 ++++++++++++-------------
1 file changed, 12 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 7d2257cc5438..8e8549ea1d70 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -820,19 +820,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
gfn = fault_ipa >> PAGE_SHIFT;
mmap_read_unlock(current->mm);
- /*
- * Permission faults just need to update the existing leaf entry,
- * and so normally don't require allocations from the memcache. The
- * only exception to this is when dirty logging is enabled at runtime
- * and a write fault needs to collapse a block entry into a table.
- */
- if (fault_status != FSC_PERM || (logging_active && write_fault)) {
- ret = kvm_mmu_topup_memory_cache(memcache,
- kvm_mmu_cache_min_pages(kvm));
- if (ret)
- return ret;
- }
-
mmu_seq = vcpu->kvm->mmu_notifier_seq;
/*
* Ensure the read of mmu_notifier_seq happens before we call
@@ -898,6 +885,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC))
prot |= KVM_PGTABLE_PROT_X;
+ /*
+ * Allocations from the memcache are required only when granule of the
+ * lookup level where a guest fault happened exceeds the vma_pagesize,
+ * which means new page tables will be created in the fault handlers.
+ */
+ if (fault_granule > vma_pagesize) {
+ ret = kvm_mmu_topup_memory_cache(memcache,
+ kvm_mmu_cache_min_pages(kvm));
+ if (ret)
+ return ret;
+ }
+
/*
* Under the premise of getting a FSC_PERM fault, we just need to relax
* permissions only if vma_pagesize equals fault_granule. Otherwise,
--
2.19.1
