[RFC PATCH 3/3] KVM: arm64: Add usage of stage 2 fault lookup level in user_mem_abort()

Yanan Wang
2020-11-30T12:20:57Z

If we get a FSC_PERM fault, just using (logging_active && writable) to determine
calling kvm_pgtable_stage2_map(). There will be two more cases we should consider.

(1) After logging_active is configged back to false from true. When we get a
FSC_PERM fault with write_fault and adjustment of hugepage is needed, we should
merge tables back to a block entry. This case is ignored by still calling
kvm_pgtable_stage2_relax_perms(), which will lead to an endless loop and guest
panic due to soft lockup.

(2) We use (FSC_PERM && logging_active && writable) to determine collapsing
a block entry into a table by calling kvm_pgtable_stage2_map(). But sometimes
we may only need to relax permissions when trying to write to a page other than
a block. In this condition, using kvm_pgtable_stage2_relax_perms() will be fine.

The ISS filed bit[1:0] in ESR_EL2 regesiter indicates the stage2 lookup level
at which a D-abort or I-abort occured. By comparing granule of the fault lookup
level with vma_pagesize, we can strictly distinguish conditions of calling
kvm_pgtable_stage2_relax_perms() or kvm_pgtable_stage2_map(), and the above
two cases will be well considered.

Suggested-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
---
arch/arm64/include/asm/esr.h | 1 +
arch/arm64/include/asm/kvm_emulate.h | 5 +++++
arch/arm64/kvm/mmu.c | 11 +++++++++--
3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 22c81f1edda2..85a3e49f92f4 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -104,6 +104,7 @@
/* Shared ISS fault status code(IFSC/DFSC) for Data/Instruction aborts */
#define ESR_ELx_FSC (0x3F)
#define ESR_ELx_FSC_TYPE (0x3C)
+#define ESR_ELx_FSC_LEVEL (0x03)
#define ESR_ELx_FSC_EXTABT (0x10)
#define ESR_ELx_FSC_SERROR (0x11)
#define ESR_ELx_FSC_ACCESS (0x08)
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 5ef2669ccd6c..2e0e8edf6306 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -350,6 +350,11 @@ static __always_inline u8 kvm_vcpu_trap_get_fault_type(const struct kvm_vcpu *vc
return kvm_vcpu_get_esr(vcpu) & ESR_ELx_FSC_TYPE;
}

+static __always_inline u8 kvm_vcpu_trap_get_fault_level(const struct kvm_vcpu *vcpu)
+{
+ return kvm_vcpu_get_esr(vcpu) & ESR_ELx_FSC_LEVEL;
+{
+
static __always_inline bool kvm_vcpu_abt_issea(const struct kvm_vcpu *vcpu)
{
switch (kvm_vcpu_trap_get_fault(vcpu)) {
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 1a01da9fdc99..75814a02d189 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -754,10 +754,12 @@ 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);
- unsigned long vma_pagesize;
+ 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;
struct kvm_pgtable *pgt;

+ fault_granule = 1UL << ARM64_HW_PGTABLE_LEVEL_SHIFT(fault_level);
write_fault = kvm_is_write_fault(vcpu);
exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu);
VM_BUG_ON(write_fault && exec_fault);
@@ -896,7 +898,12 @@ 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;

- if (fault_status == FSC_PERM && !(logging_active && writable)) {
+ /*
+ * Under the premise of getting a FSC_PERM fault, we just need to relax
+ * 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) {
ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
} else {
ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
--
2.19.1