On Mon, 17 May 2021 13:32:38 +0100,
Steven Price <steven.price@xxxxxxx> wrote:
>
> The VMM may not wish to have it's own mapping of guest memory mapped
> with PROT_MTE because this causes problems if the VMM has tag checking
> enabled (the guest controls the tags in physical RAM and it's unlikely
> the tags are correct for the VMM).
>
> Instead add a new ioctl which allows the VMM to easily read/write the
> tags from guest memory, allowing the VMM's mapping to be non-PROT_MTE
> while the VMM can still read/write the tags for the purpose of
> migration.
>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> arch/arm64/include/uapi/asm/kvm.h | 11 +++++
> arch/arm64/kvm/arm.c | 69 +++++++++++++++++++++++++++++++
> include/uapi/linux/kvm.h | 1 +
> 3 files changed, 81 insertions(+)
>
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 24223adae150..b3edde68bc3e 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -184,6 +184,17 @@ struct kvm_vcpu_events {
> __u32 reserved[12];
> };
>
> +struct kvm_arm_copy_mte_tags {
> + __u64 guest_ipa;
> + __u64 length;
> + void __user *addr;
> + __u64 flags;
> + __u64 reserved[2];
> +};
> +
> +#define KVM_ARM_TAGS_TO_GUEST 0
> +#define KVM_ARM_TAGS_FROM_GUEST 1
> +
> /* If you need to interpret the index values, here is the key: */
> #define KVM_REG_ARM_COPROC_MASK 0x000000000FFF0000
> #define KVM_REG_ARM_COPROC_SHIFT 16
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index e89a5e275e25..4b6c83beb75d 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1309,6 +1309,65 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm,
> }
> }
>
> +static int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> + struct kvm_arm_copy_mte_tags *copy_tags)
> +{
> + gpa_t guest_ipa = copy_tags->guest_ipa;
> + size_t length = copy_tags->length;
> + void __user *tags = copy_tags->addr;
> + gpa_t gfn;
> + bool write = !(copy_tags->flags & KVM_ARM_TAGS_FROM_GUEST);
> + int ret = 0;
> +
> + if (copy_tags->reserved[0] || copy_tags->reserved[1])
> + return -EINVAL;
> +
> + if (copy_tags->flags & ~KVM_ARM_TAGS_FROM_GUEST)
> + return -EINVAL;
> +
> + if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK)
> + return -EINVAL;
> +
> + gfn = gpa_to_gfn(guest_ipa);
> +
> + mutex_lock(&kvm->slots_lock);
> +
> + while (length > 0) {
> + kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL);
> + void *maddr;
> + unsigned long num_tags = PAGE_SIZE / MTE_GRANULE_SIZE;
nit: this is a compile time constant, make it a #define. This will
avoid the confusing overloading of "num_tags" as both an input and an
output for the mte_copy_tags-* functions.
> +
> + if (is_error_noslot_pfn(pfn)) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + maddr = page_address(pfn_to_page(pfn));
> +
> + if (!write) {
> + num_tags = mte_copy_tags_to_user(tags, maddr, num_tags);
> + kvm_release_pfn_clean(pfn);
> + } else {
> + num_tags = mte_copy_tags_from_user(maddr, tags,
> + num_tags);
> + kvm_release_pfn_dirty(pfn);
> + }
> +
> + if (num_tags != PAGE_SIZE / MTE_GRANULE_SIZE) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + gfn++;
> + tags += num_tags;
> + length -= PAGE_SIZE;
> + }
> +
> +out:
> + mutex_unlock(&kvm->slots_lock);
> + return ret;
> +}
> +
nit again: I'd really prefer it if you moved this to guest.c, where we
already have a bunch of the save/restore stuff.
> long kvm_arch_vm_ioctl(struct file *filp,
> unsigned int ioctl, unsigned long arg)
> {
> @@ -1345,6 +1404,16 @@ long kvm_arch_vm_ioctl(struct file *filp,
>
> return 0;
> }
> + case KVM_ARM_MTE_COPY_TAGS: {
> + struct kvm_arm_copy_mte_tags copy_tags;
> +
> + if (!kvm_has_mte(kvm))
> + return -EINVAL;
> +
> + if (copy_from_user(©_tags, argp, sizeof(copy_tags)))
> + return -EFAULT;
> + return kvm_vm_ioctl_mte_copy_tags(kvm, ©_tags);
> + }
> default:
> return -EINVAL;
> }
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 8c95ba0fadda..4c011c60d468 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1428,6 +1428,7 @@ struct kvm_s390_ucas_mapping {
> /* Available with KVM_CAP_PMU_EVENT_FILTER */
> #define KVM_SET_PMU_EVENT_FILTER _IOW(KVMIO, 0xb2, struct kvm_pmu_event_filter)
> #define KVM_PPC_SVM_OFF _IO(KVMIO, 0xb3)
> +#define KVM_ARM_MTE_COPY_TAGS _IOR(KVMIO, 0xb4, struct kvm_arm_copy_mte_tags)
>
> /* ioctl for vm fd */
> #define KVM_CREATE_DEVICE _IOWR(KVMIO, 0xe0, struct kvm_create_device)
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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