Re: [PATCH v2 2/2] arm64: kvm: Introduce MTE VCPU feature
From: Steven Price
Date: Thu Sep 10 2020 - 05:21:26 EST
On 09/09/2020 16:48, Andrew Jones wrote:
On Fri, Sep 04, 2020 at 05:00:18PM +0100, Steven Price wrote:
Add a new VCPU features 'KVM_ARM_VCPU_MTE' which enables memory tagging
on a VCPU. When enabled on any VCPU in the virtual machine this causes
all pages that are faulted into the VM to have the PG_mte_tagged flag
set (and the tag storage cleared if this is the first use).
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
arch/arm64/include/asm/kvm_emulate.h | 3 +++
arch/arm64/include/asm/kvm_host.h | 5 ++++-
arch/arm64/include/uapi/asm/kvm.h | 1 +
arch/arm64/kvm/mmu.c | 15 +++++++++++++++
arch/arm64/kvm/reset.c | 8 ++++++++
arch/arm64/kvm/sys_regs.c | 6 +++++-
6 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 49a55be2b9a2..0042323a4b7f 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -79,6 +79,9 @@ 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 (test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features))
+ 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 4f4360dd149e..b1190366242b 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -37,7 +37,7 @@
#define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
-#define KVM_VCPU_MAX_FEATURES 7
+#define KVM_VCPU_MAX_FEATURES 8
#define KVM_REQ_SLEEP \
KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
@@ -110,6 +110,9 @@ struct kvm_arch {
* supported.
*/
bool return_nisv_io_abort_to_user;
+
+ /* If any VCPU has MTE enabled then all memory must be MTE enabled */
+ bool vcpu_has_mte;
It looks like this is unnecessary as it's only used once, where a feature
check could be used.
It's used in user_mem_abort(), so every time we fault a page into the VM
- so having to iterate over all VCPUs to check if any have the feature
bit set seems too expensive.
Although perhaps I should just accept that this is realistically a VM
setting and move it out of the VCPU.
};
struct kvm_vcpu_fault_info {
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index ba85bb23f060..2677e1ab8c16 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -106,6 +106,7 @@ struct kvm_regs {
#define KVM_ARM_VCPU_SVE 4 /* enable SVE for this CPU */
#define KVM_ARM_VCPU_PTRAUTH_ADDRESS 5 /* VCPU uses address authentication */
#define KVM_ARM_VCPU_PTRAUTH_GENERIC 6 /* VCPU uses generic authentication */
+#define KVM_ARM_VCPU_MTE 7 /* VCPU supports Memory Tagging */
struct kvm_vcpu_init {
__u32 target;
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index ba00bcc0c884..e8891bacd76f 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1949,6 +1949,21 @@ 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 (system_supports_mte() && kvm->arch.vcpu_has_mte && pfn_valid(pfn)) {
+ /*
+ * VM will be able to see the page's tags, so we must ensure
+ * they have been initialised.
+ */
+ struct page *page = pfn_to_page(pfn);
+ long i, nr_pages = compound_nr(page);
+
+ /* if PG_mte_tagged is set, tags have already been initialised */
+ 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)
kvm_set_pfn_dirty(pfn);
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index ee33875c5c2a..82f3883d717f 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -274,6 +274,14 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
}
}
+ if (test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features)) {
+ if (!system_supports_mte()) {
+ ret = -EINVAL;
+ goto out;
+ }
+ vcpu->kvm->arch.vcpu_has_mte = true;
+ }
We either need a KVM cap or a new CPU feature probing interface to avoid
making userspace try features one at a time. It's too bad that VCPU_INIT
doesn't clear all offending features from the feature set when returning
EINVAL, because then userspace could create a scratch VCPU with everything
it supports in order to see what KVM also supports in one go.
If Peter's TELL_ME_WHAT_YOU_HAVE idea works out then perhaps we don't
need the cap? Or would it still be useful?
Thanks,
Steve
+
switch (vcpu->arch.target) {
default:
if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index a655f172b5ad..6a971b201e81 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1132,7 +1132,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT);
} else if (id == SYS_ID_AA64PFR1_EL1) {
- val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT);
+ if (!test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features))
+ val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT);
} else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) {
val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) |
(0xfUL << ID_AA64ISAR1_API_SHIFT) |
@@ -1394,6 +1395,9 @@ static bool access_mte_regs(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
static unsigned int mte_visibility(const struct kvm_vcpu *vcpu,
const struct sys_reg_desc *rd)
{
+ if (test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features))
+ return 0;
+
return REG_HIDDEN_USER | REG_HIDDEN_GUEST;
}
--
2.20.1
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Thanks,
drew