On 10/08/2022 20:30, Peter Collingbourne wrote:
> Previously we allowed creating a memslot containing a private mapping that
> was not VM_MTE_ALLOWED, but would later reject KVM_RUN with -EFAULT. Now
> we reject the memory region at memslot creation time.
>
> Since this is a minor tweak to the ABI (a VMM that created one of
> these memslots would fail later anyway), no VMM to my knowledge has
> MTE support yet, and the hardware with the necessary features is not
> generally available, we can probably make this ABI change at this point.
>
> Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
> ---
> arch/arm64/kvm/mmu.c | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 750a69a97994..d54be80e31dd 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1073,6 +1073,19 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
> }
> }
>
> +static bool kvm_vma_mte_allowed(struct vm_area_struct *vma)
> +{
> + /*
> + * 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 (vma->vm_flags & VM_SHARED)
> + return false;
> +
> + return vma->vm_flags & VM_MTE_ALLOWED;
> +}
> +
> 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)
> @@ -1249,9 +1262,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> }
>
> if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
> - /* Check the VMM hasn't introduced a new VM_SHARED VMA */
> - if ((vma->vm_flags & VM_MTE_ALLOWED) &&
> - !(vma->vm_flags & VM_SHARED)) {
> + /* Check the VMM hasn't introduced a new disallowed VMA */
> + if (kvm_vma_mte_allowed(vma)) {
> sanitise_mte_tags(kvm, pfn, vma_pagesize);
> } else {
> ret = -EFAULT;
> @@ -1695,12 +1707,7 @@ 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) {
> + if (kvm_has_mte(kvm) && !kvm_vma_mte_allowed(vma)) {
> ret = -EINVAL;
> break;
> }
