Re: [PATCH v4 15/21] KVM: arm64: Set an impdef ESR for Virtual-SError using VSESR_EL2.

Christoffer Dall
2017-10-30T10:50:20Z

On Mon, Oct 30, 2017 at 08:59:51AM +0100, Christoffer Dall wrote:
> On Thu, Oct 19, 2017 at 03:58:01PM +0100, James Morse wrote:
> > Prior to v8.2's RAS Extensions, the HCR_EL2.VSE 'virtual SError' feature
> > generated an SError with an implementation defined ESR_EL1.ISS, because we
> > had no mechanism to specify the ESR value.
> >
> > On Juno this generates an all-zero ESR, the most significant bit 'ISV'
> > is clear indicating the remainder of the ISS field is invalid.
> >
> > With the RAS Extensions we have a mechanism to specify this value, and the
> > most significant bit has a new meaning: 'IDS - Implementation Defined
> > Syndrome'. An all-zero SError ESR now means: 'RAS error: Uncategorized'
> > instead of 'no valid ISS'.
> >
> > Add KVM support for the VSESR_EL2 register to specify an ESR value when
> > HCR_EL2.VSE generates a virtual SError. Change kvm_inject_vabt() to
> > specify an implementation-defined value.
> >
> > We only need to restore the VSESR_EL2 value when HCR_EL2.VSE is set, KVM
> > save/restores this bit during __deactivate_traps() and hardware clears the
> > bit once the guest has consumed the virtual-SError.
> >
> > Future patches may add an API (or KVM CAP) to pend a virtual SError with
> > a specified ESR.
> >
> > Cc: Dongjiu Geng <gengdongjiu@huawei.com>
> > Signed-off-by: James Morse <james.morse@arm.com>
> > ---
> > arch/arm64/include/asm/kvm_emulate.h | 5 +++++
> > arch/arm64/include/asm/kvm_host.h | 3 +++
> > arch/arm64/include/asm/sysreg.h | 1 +
> > arch/arm64/kvm/hyp/switch.c | 4 ++++
> > arch/arm64/kvm/inject_fault.c | 13 ++++++++++++-
> > 5 files changed, 25 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index e5df3fce0008..8a7a838eb17a 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -61,6 +61,11 @@ static inline void vcpu_set_hcr(struct kvm_vcpu *vcpu, unsigned long hcr)
> > vcpu->arch.hcr_el2 = hcr;
> > }
> >
> > +static inline void vcpu_set_vsesr(struct kvm_vcpu *vcpu, u64 vsesr)
> > +{
> > + vcpu->arch.vsesr_el2 = vsesr;
> > +}
> > +
> > static inline unsigned long *vcpu_pc(const struct kvm_vcpu *vcpu)
> > {
> > return (unsigned long *)&vcpu_gp_regs(vcpu)->regs.pc;
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index a0e2f7962401..28a4de85edee 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -277,6 +277,9 @@ struct kvm_vcpu_arch {
> >
> > /* Detect first run of a vcpu */
> > bool has_run_once;
> > +
> > + /* Virtual SError ESR to restore when HCR_EL2.VSE is set */
> > + u64 vsesr_el2;
> > };
> >
> > #define vcpu_gp_regs(v) (&(v)->arch.ctxt.gp_regs)
> > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> > index 427c36bc5dd6..a493e93de296 100644
> > --- a/arch/arm64/include/asm/sysreg.h
> > +++ b/arch/arm64/include/asm/sysreg.h
> > @@ -253,6 +253,7 @@
> >
> > #define SYS_DACR32_EL2 sys_reg(3, 4, 3, 0, 0)
> > #define SYS_IFSR32_EL2 sys_reg(3, 4, 5, 0, 1)
> > +#define SYS_VSESR_EL2 sys_reg(3, 4, 5, 2, 3)
> > #define SYS_FPEXC32_EL2 sys_reg(3, 4, 5, 3, 0)
> >
> > #define __SYS__AP0Rx_EL2(x) sys_reg(3, 4, 12, 8, x)
> > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > index 945e79c641c4..af37658223a0 100644
> > --- a/arch/arm64/kvm/hyp/switch.c
> > +++ b/arch/arm64/kvm/hyp/switch.c
> > @@ -86,6 +86,10 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> > isb();
> > }
> > write_sysreg(val, hcr_el2);
> > +
> > + if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN) && (val & HCR_VSE))
> > + write_sysreg_s(vcpu->arch.vsesr_el2, SYS_VSESR_EL2);
> > +
>
> Just a heads up: If my optimization work gets merged, that will
> eventually move stuff like this in to load/put hooks for system
> registers, but I can deal with this easily, also adding a direct write
> in pend_guest_serror when moving the logic around.
>
> However, if we start architecting something more complex, it would be
> good to keep in mind how to maintain minimum work on the switching path
> after we've optimized the hypervisor.
>

Actually, after thinking about this, if the guest can only see this via
the ESR if we set the HCR_EL2.VSE, wouldn't it make sense to just set
this value in pend_guest_serror, and if we're on a non-VHE system --
assuming that's something we want to support with this 8.2 feature -- we
jump to EL2 and back to set the value?

Thanks,
-Christoffer