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Re: [PATCH v2 02/28] arm64: KVM: Hide unsupported AArch64 CPU features from guests
- From: Dave Martin <Dave dot Martin at arm dot com>
- To: Alex Bennée <alex dot bennee at linaro dot org>
- Cc: linux-arch at vger dot kernel dot org, libc-alpha at sourceware dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Marc Zyngier <marc dot zyngier at arm dot com>, Christoffer Dall <christoffer dot dall at linaro dot org>, Richard Sandiford <richard dot sandiford at arm dot com>, kvmarm at lists dot cs dot columbia dot edu, linux-arm-kernel at lists dot infradead dot org
- Date: Fri, 15 Sep 2017 01:04:24 +0100
- Subject: Re: [PATCH v2 02/28] arm64: KVM: Hide unsupported AArch64 CPU features from guests
- Authentication-results: sourceware.org; auth=none
- References: <1504198860-12951-1-git-send-email-Dave.Martin@arm.com> <1504198860-12951-3-git-send-email-Dave.Martin@arm.com> <87r2vaacll.fsf@linaro.org>
On Wed, Sep 13, 2017 at 03:37:42PM +0100, Alex Bennée wrote:
>
> Dave Martin <Dave.Martin@arm.com> writes:
[...]
> > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > index 945e79c..35a90b8 100644
> > --- a/arch/arm64/kvm/hyp/switch.c
> > +++ b/arch/arm64/kvm/hyp/switch.c
> > @@ -81,11 +81,17 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> > * it will cause an exception.
> > */
> > val = vcpu->arch.hcr_el2;
> > +
> > if (!(val & HCR_RW) && system_supports_fpsimd()) {
> > write_sysreg(1 << 30, fpexc32_el2);
> > isb();
> > }
> > +
> > + if (val & HCR_RW) /* for AArch64 only: */
> > + val |= HCR_TID3; /* TID3: trap feature register accesses */
> > +
>
> I wondered as this is the hyp switch can we make use of testing val &
> HCR_RW for both this and above. But it seems minimal in the generated
> code so probably not.
I figured that the code was cleaner ths way, since they're independent
bits of code that both happen to be applicable only to AArch64 guests.
[...]
> > +
> > + /*
> > + * ID regs: all ID_SANITISED() entries here must have corresponding
> > + * entries in arm64_ftr_regs[].
> > + */
>
> arm64_ftr_regs isn't updated in this commit. Does this break bisection?
This commit only adds ID_SANITISED() entries for regs that are already
present in arm64_ftr_regs[]. (If you spot any that are missing, give me
a shout...)
SVE only adds one new ID register, ID_AA64ZFR0_EL1 -- but SVE defines no
fields in there yet, so I just leave it ID_UNALLOCATED() which will
cause it to read as zero for the guest.
> > +
> > + /* AArch64 mappings of the AArch32 ID registers */
> > + /* CRm=1 */
> > + ID_SANITISED(ID_PFR0_EL1),
> > + ID_SANITISED(ID_PFR1_EL1),
[...]
> > + /* CRm=7 */
> > + ID_SANITISED(ID_AA64MMFR0_EL1),
> > + ID_SANITISED(ID_AA64MMFR1_EL1),
> > + ID_SANITISED(ID_AA64MMFR2_EL1),
> > + ID_UNALLOCATED(7,3),
> > + ID_UNALLOCATED(7,4),
> > + ID_UNALLOCATED(7,5),
> > + ID_UNALLOCATED(7,6),
> > + ID_UNALLOCATED(7,7),
> > +
>
> I think it might be worthwhile adding a test to kvm-unit-tests to walk
> all the ID registers to check this.
Sounds sensible, I'll take a look at that.
[...]
Cheers
---Dave