Re: [PATCH v7 13/27] KVM: arm64/sve: Context switch the SVE registers

Alex Bennée
2019-04-24T14:51:43Z

Dave Martin <Dave.Martin@arm.com> writes:

> On Thu, Apr 04, 2019 at 10:35:02AM +0200, Andrew Jones wrote:
>> On Thu, Apr 04, 2019 at 09:10:08AM +0100, Dave Martin wrote:
>> > On Wed, Apr 03, 2019 at 10:01:45PM +0200, Andrew Jones wrote:
>> > > On Fri, Mar 29, 2019 at 01:00:38PM +0000, Dave Martin wrote:
>> > > > In order to give each vcpu its own view of the SVE registers, this
>> > > > patch adds context storage via a new sve_state pointer in struct
>> > > > vcpu_arch. An additional member sve_max_vl is also added for each
>> > > > vcpu, to determine the maximum vector length visible to the guest
>> > > > and thus the value to be configured in ZCR_EL2.LEN while the vcpu
>> > > > is active. This also determines the layout and size of the storage
>> > > > in sve_state, which is read and written by the same backend
>> > > > functions that are used for context-switching the SVE state for
>> > > > host tasks.
>> > > >
>> > > > On SVE-enabled vcpus, SVE access traps are now handled by switching
>> > > > in the vcpu's SVE context and disabling the trap before returning
>> > > > to the guest. On other vcpus, the trap is not handled and an exit
>> > > > back to the host occurs, where the handle_sve() fallback path
>> > > > reflects an undefined instruction exception back to the guest,
>> > > > consistently with the behaviour of non-SVE-capable hardware (as was
>> > > > done unconditionally prior to this patch).
>> > > >
>> > > > No SVE handling is added on non-VHE-only paths, since VHE is an
>> > > > architectural and Kconfig prerequisite of SVE.
>> > > >
>> > > > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
>> > > > Reviewed-by: Julien Thierry <julien.thierry@arm.com>
>> > > > Tested-by: zhang.lei <zhang.lei@jp.fujitsu.com>
>> > > >
>> > > > ---
>> > > >
>> > > > Changes since v5:
>> > > >
>> > > > * [Julien Thierry, Julien Grall] Commit message typo fixes
>> > > >
>> > > > * [Mark Rutland] Rename trap_class to hsr_ec, for consistency with
>> > > > existing code.
>> > > >
>> > > > * [Mark Rutland] Simplify condition for refusing to handle an
>> > > > FPSIMD/SVE trap, using multiple if () statements for clarity. The
>> > > > previous condition was a bit tortuous, and how that the static_key
>> > > > checks have been hoisted out, it makes little difference to the
>> > > > compiler how we express the condition here.
>> > > > ---
>> > > > arch/arm64/include/asm/kvm_host.h | 6 ++++
>> > > > arch/arm64/kvm/fpsimd.c | 5 +--
>> > > > arch/arm64/kvm/hyp/switch.c | 75 +++++++++++++++++++++++++++++----------
>> > > > 3 files changed, 66 insertions(+), 20 deletions(-)
>> > > >
>> > > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> > > > index 22cf484..4fabfd2 100644
>> > > > --- a/arch/arm64/include/asm/kvm_host.h
>> > > > +++ b/arch/arm64/include/asm/kvm_host.h
>> > > > @@ -228,6 +228,8 @@ struct vcpu_reset_state {
>> > > >
>> > > > struct kvm_vcpu_arch {
>> > > > struct kvm_cpu_context ctxt;
>> > > > + void *sve_state;
>> > > > + unsigned int sve_max_vl;
>> > > >
>> > > > /* HYP configuration */
>> > > > u64 hcr_el2;
>> > > > @@ -323,6 +325,10 @@ struct kvm_vcpu_arch {
>> > > > bool sysregs_loaded_on_cpu;
>> > > > };
>> > > >
>> > > > +/* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
>> > > > +#define vcpu_sve_pffr(vcpu) ((void *)((char *)((vcpu)->arch.sve_state) + \
>> > > > + sve_ffr_offset((vcpu)->arch.sve_max_vl)))
>> > >
>> > > Maybe an inline function instead?
>> >
>> > I tried, but that requires the definition of struct kvm_vcpu to be
>> > visible. I failed to get that here without circular #include problems,
>> > and it looked tricky to fix.
>>
>> Ah, OK
>>
>> >
>> > Since this is a small bit of code which is unlikely to get used by
>> > accident, I decided it was OK to keep it as a macro.
>> >
>> > Can you see another way around this?
>>
>> Nope
>
> OK. If someone eventually solves this, I'd be happy to change to an
> inline function.

Is the function intended to be used by more call sites? Currently in the
tree with this plus the v2 fixups I can only see:

arch/arm64/include/asm/kvm_host.h:333:#define vcpu_sve_pffr(vcpu) ((void *)((char *)((vcpu)->arch.sve_state) + \
arch/arm64/kvm/hyp/switch.c:388: sve_load_state(vcpu_sve_pffr(vcpu),

--
Alex Bennée