On Fri, Jun 04, 2021 at 12:15:56PM +0100, Steven Price wrote:
> On 03/06/2021 18:13, Catalin Marinas wrote:
> > On Mon, May 24, 2021 at 11:45:12AM +0100, Steven Price wrote:
> >> 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..baa33359e477 100644
> >> --- a/arch/arm64/kvm/arm.c
> >> +++ b/arch/arm64/kvm/arm.c
> >> @@ -1345,6 +1345,13 @@ 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 (copy_from_user(©_tags, argp, sizeof(copy_tags)))
> >> + return -EFAULT;
> >> + return kvm_vm_ioctl_mte_copy_tags(kvm, ©_tags);
> >> + }
> >
> > I wonder whether we need an update of the user structure following a
> > fault, like how much was copied etc. In case of an error, some tags were
> > copied and the VMM may want to skip the page before continuing. But here
> > there's no such information provided.
> >
> > On the ptrace interface, we return 0 on the syscall if any bytes were
> > copied and update iov_len to such number. Maybe you want to still return
> > an error here but updating copy_tags.length would be nice (and, of
> > course, a copy_to_user() back).
>
> Good idea - as you suggest I'll make it update length with the number of
> bytes not processed. Although in general I think we're expecting the VMM
> to know where the memory is so this is more of a programming error - but
> could still be useful for debugging.
Or update it to the number of bytes copied to be consistent with
ptrace()'s iov.len. On success, the structure is effectively left
unchanged.
--
Catalin
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