arm/arm64: KVM: Use kernel mapping to perform invalidation on page fault

When handling a fault in stage-2, we need to resync I$ and D$, just
to be sure we don't leave any old cache line behind.

That's very good, except that we do so using the *user* address.
Under heavy load (swapping like crazy), we may end up in a situation
where the page gets mapped in stage-2 while being unmapped from
userspace by another CPU.

At that point, the DC/IC instructions can generate a fault, which
we handle with kvm->mmu_lock held. The box quickly deadlocks, user
is unhappy.

Instead, perform this invalidation through the kernel mapping,
which is guaranteed to be present. The box is much happier, and so
am I.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 78e68abcb01f..136662547ca6 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -957,6 +957,12 @@ static bool kvm_is_device_pfn(unsigned long pfn)
         return !pfn_valid(pfn);
 }
 
+static void coherent_cache_guest_page(struct kvm_vcpu *vcpu, pfn_t pfn,
+                                      unsigned long size, bool uncached)
+{
+        __coherent_cache_guest_page(vcpu, pfn, size, uncached);
+}
+
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                           struct kvm_memory_slot *memslot, unsigned long hva,
                           unsigned long fault_status)
@@ -1046,8 +1052,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                         kvm_set_s2pmd_writable(&new_pmd);
                         kvm_set_pfn_dirty(pfn);
                 }
-                coherent_cache_guest_page(vcpu, hva & PMD_MASK, PMD_SIZE,
-                                          fault_ipa_uncached);
+                coherent_cache_guest_page(vcpu, pfn, PMD_SIZE, fault_ipa_uncached);
                 ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
         } else {
                 pte_t new_pte = pfn_pte(pfn, mem_type);
@@ -1055,8 +1060,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                         kvm_set_s2pte_writable(&new_pte);
                         kvm_set_pfn_dirty(pfn);
                 }
-                coherent_cache_guest_page(vcpu, hva, PAGE_SIZE,
-                                          fault_ipa_uncached);
+                coherent_cache_guest_page(vcpu, pfn, PAGE_SIZE, fault_ipa_uncached);
                 ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte,
                         pgprot_val(mem_type) == pgprot_val(PAGE_S2_DEVICE));
         }