On 17/05/2021 19:04, Marc Zyngier wrote:
> On Mon, 17 May 2021 13:32:38 +0100,
> Steven Price <steven.pr...@arm.com> 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.pr...@arm.com>
>> ---
>> 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.
No problem, I agree my usage of num_tags wasn't very clear.
>> +
>> + 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.
Sure - I'll move it across.
Thanks,
Steve
