On Mon, 08 Jul 2024 18:53:39 +0100,
Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Mon, 08 Jul 2024 18:47:45 +0100,
> Marc Zyngier <maz@xxxxxxxxxx> wrote:
> >
> > On Mon, 08 Jul 2024 18:34:36 +0100,
> > Mark Brown <broonie@xxxxxxxxxx> wrote:
> > >
> > > [1 <text/plain; us-ascii (7bit)>]
> > > On Mon, Jul 08, 2024 at 04:44:34PM +0100, Marc Zyngier wrote:
> > > > Just like the rest of the FP/SIMD state, FPMR needs to be context
> > > > switched.
> > >
> > > > The only interesting thing here is that we need to treat the pKVM
> > > > part a bit differently, as the host FP state is never written back
> > > > to the vcpu thread, but instead stored locally and eagerly restored.
> > >
> > > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > > > ---
> > > > arch/arm64/include/asm/kvm_host.h | 10 ++++++++++
> > > > arch/arm64/kvm/fpsimd.c | 1 +
> > > > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 4 ++++
> > > > arch/arm64/kvm/hyp/nvhe/switch.c | 10 ++++++++++
> > > > arch/arm64/kvm/hyp/vhe/switch.c | 4 ++++
> > > > 5 files changed, 29 insertions(+)
> > >
> > > I'm possibly missing something here but I'm not seeing where we load the
> > > state for the guest, especially in the VHE case. I would expect to see
> > > a change in kvm_hyp_handle_fpsimd() to load FPMR for guests with the
> > > feature (it needs to be in there to keep in sync with the ownership
> > > tracking for the rest of the FP state, and to avoid loading needlessly
> > > in cases where the guest never touches FP).
> > >
> > > Saving for the guest was handled in the previous patch.
> > >
> > > > diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> > > > index 77010b76c150f..a307c1d5ac874 100644
> > > > --- a/arch/arm64/kvm/hyp/vhe/switch.c
> > > > +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> > > > @@ -312,6 +312,10 @@ static bool kvm_hyp_handle_eret(struct kvm_vcpu *vcpu, u64 *exit_code)
> > > > static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
> > > > {
> > > > __fpsimd_save_state(*host_data_ptr(fpsimd_state));
> > > > +
> > > > + if (system_supports_fpmr() &&
> > > > + kvm_has_feat(vcpu->kvm, ID_AA64PFR2_EL1, FPMR, IMP))
> > > > + **host_data_ptr(fpmr_ptr) = read_sysreg_s(SYS_FPMR);
> > > > }
> > >
> > > That's only saving the host state, it doesn't load the guest
> > > state.
So after cherry-picking my own fixes and realising that I had left
pKVM in the lurch, this is what I have added to this patch, which
hopefully does the right thing.
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index f59ccfe11ab9a..52c7dc8446f16 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -404,6 +404,10 @@ static bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
else
__fpsimd_restore_state(&vcpu->arch.ctxt.fp_regs);
+ if (system_supports_fpmr() &&
+ kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64PFR2_EL1, FPMR, IMP))
+ write_sysreg_s(__vcpu_sys_reg(vcpu, FPMR), SYS_FPMR);
+
/* Skip restoring fpexc32 for AArch64 guests */
if (!(read_sysreg(hcr_el2) & HCR_RW))
write_sysreg(__vcpu_sys_reg(vcpu, FPEXC32_EL2), fpexc32_el2);
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 6b14a2c13e287..97fc6ae123a03 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -62,6 +62,8 @@ static void fpsimd_sve_flush(void)
static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
{
+ bool has_fpmr;
+
if (!guest_owns_fp_regs())
return;
@@ -73,13 +75,17 @@ static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
else
__fpsimd_save_state(&vcpu->arch.ctxt.fp_regs);
+ has_fpmr = (system_supports_fpmr() &&
+ kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64PFR2_EL1, FPMR, IMP));
+ if (has_fpmr)
+ __vcpu_sys_reg(vcpu, FPMR) = read_sysreg_s(SYS_FPMR);
+
if (system_supports_sve())
__hyp_sve_restore_host();
else
__fpsimd_restore_state(*host_data_ptr(fpsimd_state));
- if (system_supports_fpmr() &&
- kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64PFR2_EL1, FPMR, IMP))
+ if (has_fpmr)
write_sysreg_s(*host_data_ptr(fpmr), SYS_FPMR);
*host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
I'll repost the series after -rc1.
M.
--
Without deviation from the norm, progress is not possible.
