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[PATCH v9 2/6] arm64: kvm: Introduce MTE VM feature

Steven Price posted 6 patches 4 years, 11 months ago
There is a newer version of this series
[PATCH v9 2/6] arm64: kvm: Introduce MTE VM feature
Posted by Steven Price 4 years, 11 months ago 
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 <steven.price@arm.com>
---
 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                 | 16 ++++++++++++++++
 arch/arm64/kvm/sys_regs.c            |  3 ++-
 include/uapi/linux/kvm.h             |  1 +
 6 files changed, 27 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 3d10e6527f7d..1170ee137096 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 {
@@ -767,6 +769,7 @@ 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 77cb2d28f2a4..fdb6ab604fd0 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -879,6 +879,22 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (vma_pagesize == PAGE_SIZE && !force_pte)
 		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
 							   &pfn, &fault_ipa);
+
+	if (kvm_has_mte(kvm) && pfn_valid(pfn)) {
+		/*
+		 * VM will be able to see the page's tags, so we must ensure
+		 * they have been initialised. if PG_mte_tagged is set, tags
+		 * have already been initialised.
+		 */
+		struct page *page = pfn_to_page(pfn);
+		unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT;
+
+		for (i = 0; i < nr_pages; i++, page++) {
+			if (!test_and_set_bit(PG_mte_tagged, &page->flags))
+				mte_clear_page_tags(page_address(page));
+		}
+	}
+
 	if (writable)
 		prot |= KVM_PGTABLE_PROT_W;
 
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 4f2f1e3145de..e09dbc00b0a2 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1046,7 +1046,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		val |= FIELD_PREP(FEATURE(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3);
 		break;
 	case SYS_ID_AA64PFR1_EL1:
-		val &= ~FEATURE(ID_AA64PFR1_MTE);
+		if (!kvm_has_mte(vcpu->kvm))
+			val &= ~FEATURE(ID_AA64PFR1_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 8b281f722e5b..05618a4abf7e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1078,6 +1078,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_DIRTY_LOG_RING 192
 #define KVM_CAP_X86_BUS_LOCK_EXIT 193
 #define KVM_CAP_PPC_DAWR1 194
+#define KVM_CAP_ARM_MTE 195
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.20.1
Re: [PATCH v9 2/6] arm64: kvm: Introduce MTE VM feature
Posted by Marc Zyngier 4 years, 11 months ago 
On Mon, 01 Mar 2021 14:23:11 +0000,
Steven Price <steven.price@arm.com> 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 <steven.price@arm.com>
> ---
>  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                 | 16 ++++++++++++++++
>  arch/arm64/kvm/sys_regs.c            |  3 ++-
>  include/uapi/linux/kvm.h             |  1 +
>  6 files changed, 27 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 3d10e6527f7d..1170ee137096 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 {
> @@ -767,6 +769,7 @@ 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 77cb2d28f2a4..fdb6ab604fd0 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -879,6 +879,22 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (vma_pagesize == PAGE_SIZE && !force_pte)
>  		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
>  							   &pfn, &fault_ipa);
> +
> +	if (kvm_has_mte(kvm) && pfn_valid(pfn)) {
> +		/*
> +		 * VM will be able to see the page's tags, so we must ensure
> +		 * they have been initialised. if PG_mte_tagged is set, tags
> +		 * have already been initialised.
> +		 */
> +		struct page *page = pfn_to_page(pfn);
> +		unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT;
> +
> +		for (i = 0; i < nr_pages; i++, page++) {
> +			if (!test_and_set_bit(PG_mte_tagged, &page->flags))
> +				mte_clear_page_tags(page_address(page));
> +		}
> +	}

Is there any reason to do this dance for anything but a translation
fault?

> +
>  	if (writable)
>  		prot |= KVM_PGTABLE_PROT_W;
>  
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 4f2f1e3145de..e09dbc00b0a2 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1046,7 +1046,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>  		val |= FIELD_PREP(FEATURE(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3);
>  		break;
>  	case SYS_ID_AA64PFR1_EL1:
> -		val &= ~FEATURE(ID_AA64PFR1_MTE);
> +		if (!kvm_has_mte(vcpu->kvm))
> +			val &= ~FEATURE(ID_AA64PFR1_MTE);

Are we happy to expose *any* of the MTE flavours? Or should we
restrict it in any way?

>  		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 8b281f722e5b..05618a4abf7e 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1078,6 +1078,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_DIRTY_LOG_RING 192
>  #define KVM_CAP_X86_BUS_LOCK_EXIT 193
>  #define KVM_CAP_PPC_DAWR1 194
> +#define KVM_CAP_ARM_MTE 195
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> -- 
> 2.20.1
> 
> 

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
Re: [PATCH v9 2/6] arm64: kvm: Introduce MTE VM feature
Posted by Steven Price 4 years, 11 months ago 
On 09/03/2021 17:06, Marc Zyngier wrote:
> On Mon, 01 Mar 2021 14:23:11 +0000,
> Steven Price <steven.price@arm.com> 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 <steven.price@arm.com>
>> ---
>>   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                 | 16 ++++++++++++++++
>>   arch/arm64/kvm/sys_regs.c            |  3 ++-
>>   include/uapi/linux/kvm.h             |  1 +
>>   6 files changed, 27 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 3d10e6527f7d..1170ee137096 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 {
>> @@ -767,6 +769,7 @@ 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 77cb2d28f2a4..fdb6ab604fd0 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -879,6 +879,22 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>   	if (vma_pagesize == PAGE_SIZE && !force_pte)
>>   		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
>>   							   &pfn, &fault_ipa);
>> +
>> +	if (kvm_has_mte(kvm) && pfn_valid(pfn)) {
>> +		/*
>> +		 * VM will be able to see the page's tags, so we must ensure
>> +		 * they have been initialised. if PG_mte_tagged is set, tags
>> +		 * have already been initialised.
>> +		 */
>> +		struct page *page = pfn_to_page(pfn);
>> +		unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT;
>> +
>> +		for (i = 0; i < nr_pages; i++, page++) {
>> +			if (!test_and_set_bit(PG_mte_tagged, &page->flags))
>> +				mte_clear_page_tags(page_address(page));
>> +		}
>> +	}
> 
> Is there any reason to do this dance for anything but a translation
> fault?

Good point I guess this should have a (fault_status != FSC_PERM) in the 
test to match the other paths.

>> +
>>   	if (writable)
>>   		prot |= KVM_PGTABLE_PROT_W;
>>   
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 4f2f1e3145de..e09dbc00b0a2 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -1046,7 +1046,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>>   		val |= FIELD_PREP(FEATURE(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3);
>>   		break;
>>   	case SYS_ID_AA64PFR1_EL1:
>> -		val &= ~FEATURE(ID_AA64PFR1_MTE);
>> +		if (!kvm_has_mte(vcpu->kvm))
>> +			val &= ~FEATURE(ID_AA64PFR1_MTE);
> 
> Are we happy to expose *any* of the MTE flavours? Or should we
> restrict it in any way?

Another good point - it would make sense to restrict this in case 
another MTE flavour is invented.

Thanks,

Steve

>>   		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 8b281f722e5b..05618a4abf7e 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1078,6 +1078,7 @@ struct kvm_ppc_resize_hpt {
>>   #define KVM_CAP_DIRTY_LOG_RING 192
>>   #define KVM_CAP_X86_BUS_LOCK_EXIT 193
>>   #define KVM_CAP_PPC_DAWR1 194
>> +#define KVM_CAP_ARM_MTE 195
>>   
>>   #ifdef KVM_CAP_IRQ_ROUTING
>>   
>> -- 
>> 2.20.1
>>
>>
> 
> Thanks,
> 
> 	M.
>

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