This series adds support for using the Arm Memory Tagging Extensions
(MTE) in a KVM guest.
This time with less BKL but hopefully no new races!
Changes since v15[1]:
- Prevent VM_SHARED mappings with an MTE-enabled VM.
- Dropped the mte_prepare_page_tags() function, sanitise_mte_tags() now
does the PG_mte_tagged dance without extra locks.
- Added a comment to sanitise_mte_tags() explaining why the apparent
race with the test/set of page->flags is safe.
- Added a sentence to kvm/api.rst explaining that VM_SHARED is not
permitted when used with MTE in a guest.
- Dropped the Reviewed-by tags on patches 3 and 7 due to the changes.
[1] https://lore.kernel.org/r/20210614090525.4338-1-steven.price%40arm.com
Steven Price (7):
arm64: mte: Handle race when synchronising tags
arm64: mte: Sync tags for pages where PTE is untagged
KVM: arm64: Introduce MTE VM feature
KVM: arm64: Save/restore MTE registers
KVM: arm64: Expose KVM_ARM_CAP_MTE
KVM: arm64: ioctl to fetch/store tags in a guest
KVM: arm64: Document MTE capability and ioctl
Documentation/virt/kvm/api.rst | 61 ++++++++++++++++
arch/arm64/include/asm/kvm_arm.h | 3 +-
arch/arm64/include/asm/kvm_emulate.h | 3 +
arch/arm64/include/asm/kvm_host.h | 12 ++++
arch/arm64/include/asm/kvm_mte.h | 66 +++++++++++++++++
arch/arm64/include/asm/mte-def.h | 1 +
arch/arm64/include/asm/mte.h | 4 +-
arch/arm64/include/asm/pgtable.h | 22 +++++-
arch/arm64/include/asm/sysreg.h | 3 +-
arch/arm64/include/uapi/asm/kvm.h | 11 +++
arch/arm64/kernel/asm-offsets.c | 2 +
arch/arm64/kernel/mte.c | 37 ++++++++--
arch/arm64/kvm/arm.c | 16 +++++
arch/arm64/kvm/guest.c | 82 ++++++++++++++++++++++
arch/arm64/kvm/hyp/entry.S | 7 ++
arch/arm64/kvm/hyp/exception.c | 3 +-
arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 21 ++++++
arch/arm64/kvm/mmu.c | 62 +++++++++++++++-
arch/arm64/kvm/reset.c | 3 +-
arch/arm64/kvm/sys_regs.c | 32 +++++++--
include/uapi/linux/kvm.h | 2 +
21 files changed, 432 insertions(+), 21 deletions(-)
create mode 100644 arch/arm64/include/asm/kvm_mte.h
--
2.20.1
Add a new VM feature 'KVM_ARM_CAP_MTE' which enables memory tagging
for a VM. This will expose the feature to the guest and automatically
tag memory pages touched by the VM as PG_mte_tagged (and clear the tag
storage) to ensure that the guest cannot see stale tags, and so that
the tags are correctly saved/restored across swap.
Actually exposing the new capability to user space happens in a later
patch.
Signed-off-by: Steven Price <[email protected]>
---
arch/arm64/include/asm/kvm_emulate.h | 3 ++
arch/arm64/include/asm/kvm_host.h | 3 ++
arch/arm64/kvm/hyp/exception.c | 3 +-
arch/arm64/kvm/mmu.c | 62 +++++++++++++++++++++++++++-
arch/arm64/kvm/sys_regs.c | 7 ++++
include/uapi/linux/kvm.h | 1 +
6 files changed, 77 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index f612c090f2e4..6bf776c2399c 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -84,6 +84,9 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) ||
vcpu_el1_is_32bit(vcpu))
vcpu->arch.hcr_el2 |= HCR_TID2;
+
+ if (kvm_has_mte(vcpu->kvm))
+ vcpu->arch.hcr_el2 |= HCR_ATA;
}
static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 7cd7d5c8c4bc..afaa5333f0e4 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -132,6 +132,8 @@ struct kvm_arch {
u8 pfr0_csv2;
u8 pfr0_csv3;
+ /* Memory Tagging Extension enabled for the guest */
+ bool mte_enabled;
};
struct kvm_vcpu_fault_info {
@@ -769,6 +771,7 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
#define kvm_arm_vcpu_sve_finalized(vcpu) \
((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED)
+#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled)
#define kvm_vcpu_has_pmu(vcpu) \
(test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features))
diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
index 73629094f903..56426565600c 100644
--- a/arch/arm64/kvm/hyp/exception.c
+++ b/arch/arm64/kvm/hyp/exception.c
@@ -112,7 +112,8 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
new |= (old & PSR_C_BIT);
new |= (old & PSR_V_BIT);
- // TODO: TCO (if/when ARMv8.5-MemTag is exposed to guests)
+ if (kvm_has_mte(vcpu->kvm))
+ new |= PSR_TCO_BIT;
new |= (old & PSR_DIT_BIT);
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index c5d1f3c87dbd..f5305b7561ad 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -822,6 +822,45 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
return PAGE_SIZE;
}
+/*
+ * The page will be mapped in stage 2 as Normal Cacheable, so the VM will be
+ * able to see the page's tags and therefore they must be initialised first. If
+ * PG_mte_tagged is set, tags have already been initialised.
+ *
+ * The race in the test/set of the PG_mte_tagged flag is handled by:
+ * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs
+ * racing to santise the same page
+ * - mmap_lock protects between a VM faulting a page in and the VMM performing
+ * an mprotect() to add VM_MTE
+ */
+static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
+ unsigned long size)
+{
+ unsigned long i, nr_pages = size >> PAGE_SHIFT;
+ struct page *page;
+
+ if (!kvm_has_mte(kvm))
+ return 0;
+
+ /*
+ * pfn_to_online_page() is used to reject ZONE_DEVICE pages
+ * that may not support tags.
+ */
+ page = pfn_to_online_page(pfn);
+
+ if (!page)
+ return -EFAULT;
+
+ for (i = 0; i < nr_pages; i++, page++) {
+ if (!test_bit(PG_mte_tagged, &page->flags)) {
+ mte_clear_page_tags(page_address(page));
+ set_bit(PG_mte_tagged, &page->flags);
+ }
+ }
+
+ return 0;
+}
+
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)
@@ -971,8 +1010,16 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (writable)
prot |= KVM_PGTABLE_PROT_W;
- if (fault_status != FSC_PERM && !device)
+ if (fault_status != FSC_PERM && !device) {
+ /* Check the VMM hasn't introduced a new VM_SHARED VMA */
+ if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED)
+ return -EINVAL;
+ ret = sanitise_mte_tags(kvm, pfn, vma_pagesize);
+ if (ret)
+ goto out_unlock;
+
clean_dcache_guest_page(pfn, vma_pagesize);
+ }
if (exec_fault) {
prot |= KVM_PGTABLE_PROT_X;
@@ -1168,12 +1215,17 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
kvm_pfn_t pfn = pte_pfn(range->pte);
+ int ret;
if (!kvm->arch.mmu.pgt)
return 0;
WARN_ON(range->end - range->start != 1);
+ ret = sanitise_mte_tags(kvm, pfn, PAGE_SIZE);
+ if (ret)
+ return false;
+
/*
* We've moved a page around, probably through CoW, so let's treat it
* just like a translation fault and clean the cache to the PoC.
@@ -1381,6 +1433,14 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
if (!vma)
break;
+ /*
+ * VM_SHARED mappings are not allowed with MTE to avoid races
+ * when updating the PG_mte_tagged page flag, see
+ * sanitise_mte_tags for more details.
+ */
+ if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED)
+ return -EINVAL;
+
/*
* Take the intersection of this VMA with the memory region
*/
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 76ea2800c33e..4a98902eaf1a 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1047,6 +1047,13 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
break;
case SYS_ID_AA64PFR1_EL1:
val &= ~FEATURE(ID_AA64PFR1_MTE);
+ if (kvm_has_mte(vcpu->kvm)) {
+ u64 pfr, mte;
+
+ pfr = read_sanitised_ftr_reg(SYS_ID_AA64PFR1_EL1);
+ mte = cpuid_feature_extract_unsigned_field(pfr, ID_AA64PFR1_MTE_SHIFT);
+ val |= FIELD_PREP(FEATURE(ID_AA64PFR1_MTE), mte);
+ }
break;
case SYS_ID_AA64ISAR1_EL1:
if (!vcpu_has_ptrauth(vcpu))
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 3fd9a7e9d90c..8c95ba0fadda 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1082,6 +1082,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_SGX_ATTRIBUTE 196
#define KVM_CAP_VM_COPY_ENC_CONTEXT_FROM 197
#define KVM_CAP_PTP_KVM 198
+#define KVM_CAP_ARM_MTE 199
#ifdef KVM_CAP_IRQ_ROUTING
--
2.20.1
On Fri, 18 Jun 2021 14:28:22 +0100,
Steven Price <[email protected]> wrote:
>
> Add a new VM feature 'KVM_ARM_CAP_MTE' which enables memory tagging
> for a VM. This will expose the feature to the guest and automatically
> tag memory pages touched by the VM as PG_mte_tagged (and clear the tag
> storage) to ensure that the guest cannot see stale tags, and so that
> the tags are correctly saved/restored across swap.
>
> Actually exposing the new capability to user space happens in a later
> patch.
>
> Signed-off-by: Steven Price <[email protected]>
> ---
> arch/arm64/include/asm/kvm_emulate.h | 3 ++
> arch/arm64/include/asm/kvm_host.h | 3 ++
> arch/arm64/kvm/hyp/exception.c | 3 +-
> arch/arm64/kvm/mmu.c | 62 +++++++++++++++++++++++++++-
> arch/arm64/kvm/sys_regs.c | 7 ++++
> include/uapi/linux/kvm.h | 1 +
> 6 files changed, 77 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index f612c090f2e4..6bf776c2399c 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -84,6 +84,9 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
> if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) ||
> vcpu_el1_is_32bit(vcpu))
> vcpu->arch.hcr_el2 |= HCR_TID2;
> +
> + if (kvm_has_mte(vcpu->kvm))
> + vcpu->arch.hcr_el2 |= HCR_ATA;
> }
>
> static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 7cd7d5c8c4bc..afaa5333f0e4 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -132,6 +132,8 @@ struct kvm_arch {
>
> u8 pfr0_csv2;
> u8 pfr0_csv3;
> + /* Memory Tagging Extension enabled for the guest */
> + bool mte_enabled;
> };
>
> struct kvm_vcpu_fault_info {
> @@ -769,6 +771,7 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
> #define kvm_arm_vcpu_sve_finalized(vcpu) \
> ((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED)
>
> +#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled)
> #define kvm_vcpu_has_pmu(vcpu) \
> (test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features))
>
> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
> index 73629094f903..56426565600c 100644
> --- a/arch/arm64/kvm/hyp/exception.c
> +++ b/arch/arm64/kvm/hyp/exception.c
> @@ -112,7 +112,8 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
> new |= (old & PSR_C_BIT);
> new |= (old & PSR_V_BIT);
>
> - // TODO: TCO (if/when ARMv8.5-MemTag is exposed to guests)
> + if (kvm_has_mte(vcpu->kvm))
> + new |= PSR_TCO_BIT;
>
> new |= (old & PSR_DIT_BIT);
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index c5d1f3c87dbd..f5305b7561ad 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -822,6 +822,45 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
> return PAGE_SIZE;
> }
>
> +/*
> + * The page will be mapped in stage 2 as Normal Cacheable, so the VM will be
> + * able to see the page's tags and therefore they must be initialised first. If
> + * PG_mte_tagged is set, tags have already been initialised.
> + *
> + * The race in the test/set of the PG_mte_tagged flag is handled by:
> + * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs
> + * racing to santise the same page
> + * - mmap_lock protects between a VM faulting a page in and the VMM performing
> + * an mprotect() to add VM_MTE
> + */
> +static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
> + unsigned long size)
> +{
> + unsigned long i, nr_pages = size >> PAGE_SHIFT;
> + struct page *page;
> +
> + if (!kvm_has_mte(kvm))
> + return 0;
> +
> + /*
> + * pfn_to_online_page() is used to reject ZONE_DEVICE pages
> + * that may not support tags.
> + */
> + page = pfn_to_online_page(pfn);
> +
> + if (!page)
> + return -EFAULT;
> +
> + for (i = 0; i < nr_pages; i++, page++) {
> + if (!test_bit(PG_mte_tagged, &page->flags)) {
> + mte_clear_page_tags(page_address(page));
> + set_bit(PG_mte_tagged, &page->flags);
> + }
> + }
> +
> + return 0;
> +}
> +
> 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)
> @@ -971,8 +1010,16 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (writable)
> prot |= KVM_PGTABLE_PROT_W;
>
> - if (fault_status != FSC_PERM && !device)
> + if (fault_status != FSC_PERM && !device) {
> + /* Check the VMM hasn't introduced a new VM_SHARED VMA */
> + if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED)
> + return -EINVAL;
nit: I'd rather we return -EFAULT here. That's consistent with other
cases where we can't satisfy the mapping.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
On 21/06/2021 10:01, Marc Zyngier wrote:
> On Fri, 18 Jun 2021 14:28:22 +0100,
> Steven Price <[email protected]> wrote:
>>
>> Add a new VM feature 'KVM_ARM_CAP_MTE' which enables memory tagging
>> for a VM. This will expose the feature to the guest and automatically
>> tag memory pages touched by the VM as PG_mte_tagged (and clear the tag
>> storage) to ensure that the guest cannot see stale tags, and so that
>> the tags are correctly saved/restored across swap.
>>
>> Actually exposing the new capability to user space happens in a later
>> patch.
>>
>> Signed-off-by: Steven Price <[email protected]>
>> ---
>> arch/arm64/include/asm/kvm_emulate.h | 3 ++
>> arch/arm64/include/asm/kvm_host.h | 3 ++
>> arch/arm64/kvm/hyp/exception.c | 3 +-
>> arch/arm64/kvm/mmu.c | 62 +++++++++++++++++++++++++++-
>> arch/arm64/kvm/sys_regs.c | 7 ++++
>> include/uapi/linux/kvm.h | 1 +
>> 6 files changed, 77 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index f612c090f2e4..6bf776c2399c 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -84,6 +84,9 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
>> if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) ||
>> vcpu_el1_is_32bit(vcpu))
>> vcpu->arch.hcr_el2 |= HCR_TID2;
>> +
>> + if (kvm_has_mte(vcpu->kvm))
>> + vcpu->arch.hcr_el2 |= HCR_ATA;
>> }
>>
>> static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 7cd7d5c8c4bc..afaa5333f0e4 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -132,6 +132,8 @@ struct kvm_arch {
>>
>> u8 pfr0_csv2;
>> u8 pfr0_csv3;
>> + /* Memory Tagging Extension enabled for the guest */
>> + bool mte_enabled;
>> };
>>
>> struct kvm_vcpu_fault_info {
>> @@ -769,6 +771,7 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
>> #define kvm_arm_vcpu_sve_finalized(vcpu) \
>> ((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED)
>>
>> +#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled)
>> #define kvm_vcpu_has_pmu(vcpu) \
>> (test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features))
>>
>> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
>> index 73629094f903..56426565600c 100644
>> --- a/arch/arm64/kvm/hyp/exception.c
>> +++ b/arch/arm64/kvm/hyp/exception.c
>> @@ -112,7 +112,8 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
>> new |= (old & PSR_C_BIT);
>> new |= (old & PSR_V_BIT);
>>
>> - // TODO: TCO (if/when ARMv8.5-MemTag is exposed to guests)
>> + if (kvm_has_mte(vcpu->kvm))
>> + new |= PSR_TCO_BIT;
>>
>> new |= (old & PSR_DIT_BIT);
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index c5d1f3c87dbd..f5305b7561ad 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -822,6 +822,45 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
>> return PAGE_SIZE;
>> }
>>
>> +/*
>> + * The page will be mapped in stage 2 as Normal Cacheable, so the VM will be
>> + * able to see the page's tags and therefore they must be initialised first. If
>> + * PG_mte_tagged is set, tags have already been initialised.
>> + *
>> + * The race in the test/set of the PG_mte_tagged flag is handled by:
>> + * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs
>> + * racing to santise the same page
>> + * - mmap_lock protects between a VM faulting a page in and the VMM performing
>> + * an mprotect() to add VM_MTE
>> + */
>> +static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
>> + unsigned long size)
>> +{
>> + unsigned long i, nr_pages = size >> PAGE_SHIFT;
>> + struct page *page;
>> +
>> + if (!kvm_has_mte(kvm))
>> + return 0;
>> +
>> + /*
>> + * pfn_to_online_page() is used to reject ZONE_DEVICE pages
>> + * that may not support tags.
>> + */
>> + page = pfn_to_online_page(pfn);
>> +
>> + if (!page)
>> + return -EFAULT;
>> +
>> + for (i = 0; i < nr_pages; i++, page++) {
>> + if (!test_bit(PG_mte_tagged, &page->flags)) {
>> + mte_clear_page_tags(page_address(page));
>> + set_bit(PG_mte_tagged, &page->flags);
>> + }
>> + }
>> +
>> + return 0;
>> +}
>> +
>> 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)
>> @@ -971,8 +1010,16 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> if (writable)
>> prot |= KVM_PGTABLE_PROT_W;
>>
>> - if (fault_status != FSC_PERM && !device)
>> + if (fault_status != FSC_PERM && !device) {
>> + /* Check the VMM hasn't introduced a new VM_SHARED VMA */
>> + if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED)
>> + return -EINVAL;
>
> nit: I'd rather we return -EFAULT here. That's consistent with other
> cases where we can't satisfy the mapping.
Sure, and it would be even better if I dropped the lock (goto
out_unlock) - I'll fix that too!
Thanks,
Steve