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Mon, 08 Jul 2024 18:53:40 +0100 Date: Mon, 08 Jul 2024 18:53:39 +0100 Message-ID: <8634oj4voc.wl-maz@kernel.org> From: Marc Zyngier To: Mark Brown Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, James Morse , Suzuki K Poulose , Oliver Upton , Zenghui Yu , Fuad Tabba , Joey Gouly Subject: Re: [PATCH 3/7] KVM: arm64: Add save/restore support for FPMR In-Reply-To: <864j8z4vy6.wl-maz@kernel.org> References: <20240708154438.1218186-1-maz@kernel.org> <20240708154438.1218186-4-maz@kernel.org> <864j8z4vy6.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.3 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: broonie@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, oliver.upton@linux.dev, yuzenghui@huawei.com, tabba@google.com, joey.gouly@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240708_105344_980103_84768A30 X-CRM114-Status: GOOD ( 33.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 08 Jul 2024 18:47:45 +0100, Marc Zyngier wrote: > > On Mon, 08 Jul 2024 18:34:36 +0100, > Mark Brown wrote: > > > > [1 ] > > 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 > > > --- > > > 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. > > Ah, I forgot to cherry-pick the fixes. Fsck knows what else I forgot. > Thanks for reminding me. > > M. > > 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); > And thinking of it, that's not enough. I'm missing the pKVM angle that needs to be special cased. Drat. M. -- Without deviation from the norm, progress is not possible.