On Thu, Apr 25, 2019 at 01:30:29PM +0100, Alex Bennée wrote:
>
> Dave Martin <Dave.Martin@xxxxxxx> writes:
>
> > Currently, the way error codes are generated when processing the
> > SVE register access ioctls in a bit haphazard.
> >
> > This patch refactors the code so that the behaviour is more
> > consistent: now, -EINVAL should be returned only for unrecognised
> > register IDs or when some other runtime error occurs. -ENOENT is
> > returned for register IDs that are recognised, but whose
> > corresponding register (or slice) does not exist for the vcpu.
> >
> > To this end, in {get,set}_sve_reg() we now delegate the
> > vcpu_has_sve() check down into {get,set}_sve_vls() and
> > sve_reg_to_region(). The KVM_REG_ARM64_SVE_VLS special case is
> > picked off first, then sve_reg_to_region() plays the role of
> > exhaustively validating or rejecting the register ID and (where
> > accepted) computing the applicable register region as before.
> >
> > sve_reg_to_region() is rearranged so that -ENOENT or -EPERM is not
> > returned prematurely, before checking whether reg->id is in a
> > recognised range.
> >
> > -EPERM is now only returned when an attempt is made to access an
> > actually existing register slice on an unfinalized vcpu.
> >
> > Fixes: e1c9c98345b3 ("KVM: arm64/sve: Add SVE support to register access ioctl interface")
> > Fixes: 9033bba4b535 ("KVM: arm64/sve: Add pseudo-register for the guest's vector lengths")
> > Suggested-by: Andrew Jones <drjones@xxxxxxxxxx>
> > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
> > Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
[...]
> > @@ -335,25 +344,30 @@ static int sve_reg_to_region(struct sve_state_reg_region *region,
> > /* Verify that we match the UAPI header: */
> > BUILD_BUG_ON(SVE_NUM_SLICES != KVM_ARM64_SVE_MAX_SLICES);
> >
> > - if ((reg->id & SVE_REG_SLICE_MASK) > 0)
> > - return -ENOENT;
> > -
> > - vq = sve_vq_from_vl(vcpu->arch.sve_max_vl);
> > -
> > reg_num = (reg->id & SVE_REG_ID_MASK) >> SVE_REG_ID_SHIFT;
> >
> > if (reg->id >= zreg_id_min && reg->id <= zreg_id_max) {
> > + if (!vcpu_has_sve(vcpu) || (reg->id & SVE_REG_SLICE_MASK) > 0)
> > + return -ENOENT;
> > +
> > + vq = sve_vq_from_vl(vcpu->arch.sve_max_vl);
> > +
> > reqoffset = SVE_SIG_ZREG_OFFSET(vq, reg_num) -
> > SVE_SIG_REGS_OFFSET;
> > reqlen = KVM_SVE_ZREG_SIZE;
> > maxlen = SVE_SIG_ZREG_SIZE(vq);
> > } else if (reg->id >= preg_id_min && reg->id <= preg_id_max) {
> > + if (!vcpu_has_sve(vcpu) || (reg->id & SVE_REG_SLICE_MASK) > 0)
> > + return -ENOENT;
> > +
> > + vq = sve_vq_from_vl(vcpu->arch.sve_max_vl);
> > +
>
> I suppose you could argue for a:
>
> if (reg->id >= zreg_id_min && reg->id <= preg_id_max) {
> if (!vcpu_has_sve(vcpu) || (reg->id & SVE_REG_SLICE_MASK) > 0)
> return -ENOENT;
>
> vq = sve_vq_from_vl(vcpu->arch.sve_max_vl);
>
> if (reg->id <= zreg_id_max) {
> reqoffset = SVE_SIG_ZREG_OFFSET(vq, reg_num) -
> SVE_SIG_REGS_OFFSET;
> reqlen = KVM_SVE_ZREG_SIZE;
> maxlen = SVE_SIG_ZREG_SIZE(vq);
> } else {
> reqoffset = SVE_SIG_PREG_OFFSET(vq, reg_num) -
> SVE_SIG_REGS_OFFSET;
> reqlen = KVM_SVE_PREG_SIZE;
> maxlen = SVE_SIG_PREG_SIZE(vq);
> }
> } else {
> return -EINVAL;
> }
>
> but only for minimal DRY reasons.
Agreed, but that bakes in another assumption: that the ZREG and PREG ID
ranges are contiguous.
I preferred to keep the number of assumptions down.
Althoug the resulting code wasn't ideal, the actual amount of
duplication that I ended up with here seemed low enough as to be
acceptable (though opinions can differ on that).
[...]
Cheers
---Dave
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