Re: [PATCH v5 13/26] KVM: arm64/sve: System register context switch and access support

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Hi Dave,

On 2/26/19 5:01 PM, Dave Martin wrote:
On Tue, Feb 26, 2019 at 04:32:30PM +0000, Julien Grall wrote:
On 18/02/2019 19:52, Dave Martin wrote:
We seem to already have code for handling invariant registers as well as
reading ID register. I guess the only reason you can't use them is because
of the check the vcpu is using SVE.

However, AFAICT the restrictions callback would prevent you to enter the
{get, set}_id if the vCPU does not support SVE. So the check should not be
reachable.

Hmmm, those checks were inherited from before this refactoring.

You're right: the checks are now done a common place, so the checks in
the actual accessors should be redundant.

I could demote them to WARN(), but it may make sense simply to delete
them.

I think removing the WARN() would be best as it would avoid to introduce most of the wrappers for the registers.


The access_id_aa64zfr0_el1() should still be reachable, since we don't
have REG_NO_GUEST for this.

__access_id_reg is taking a boolean to tell whether the register is RAZ or not. So you probably could re-use it passing !vcpu_has_sve(vcpu).

It feels to me we would introduce a new restriction to tell whether the register should be RAZ. Anyway, the new restriction is probably for a follow-up patch.

Cheers,

--
Julien Grall
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