Re: [RFC PATCH 3/3] KVM: arm64: Add usage of stage 2 fault lookup level in user_mem_abort()
Hi Will,
On 2020/11/30 21:49, Will Deacon wrote:
On Mon, Nov 30, 2020 at 08:18:47PM +0800, Yanan Wang wrote:
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
Signed-off-by: Yanan Wang
---
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);
I like the idea, but is this macro reliable for stage-2 page-tables, given
that we could have a concatenated pgd?
Will
.
Yes, it's fine even when we have a concatenated pgd table.
No matter a concatenated pgd will be made or not, the initial lookup
level (start _level) is set in VTCR_EL2 register.
The MMU hardware walker will know the start_level according to
information in VTCR_EL2.
This idea runs well in practice on host where ia_bits is 40, PAGE_SIZE
is 4k, and a concatenated pgd is made for guest stage2.
According to the kernel info printed, the start_level is 1, and stage 2
translation runs as expected.
Yanan
Re: [RFC PATCH 3/3] KVM: arm64: Add usage of stage 2 fault lookup level in user_mem_abort()
On Mon, Nov 30, 2020 at 08:18:47PM +0800, Yanan Wang wrote:
> 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
> Signed-off-by: Yanan Wang
> ---
> 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);
I like the idea, but is this macro reliable for stage-2 page-tables, given
that we could have a concatenated pgd?
Will
[RFC PATCH 3/3] KVM: arm64: Add usage of stage 2 fault lookup level in user_mem_abort()
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
Signed-off-by: Yanan Wang
---
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
