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Tue, 30 Sep 2025 12:05:05 +0000 Date: Tue, 30 Sep 2025 13:05:05 +0100 Message-ID: <86tt0kywlq.wl-maz@kernel.org> From: Marc Zyngier To: Joey Gouly Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, Suzuki K Poulose , Oliver Upton , Zenghui Yu Subject: Re: [PATCH 08/13] KVM: arm64: Move CNT*CT_EL0 userspace accessors to generic infrastructure In-Reply-To: <20250930104552.GB1093338@e124191.cambridge.arm.com> References: <20250929160458.3351788-1-maz@kernel.org> <20250929160458.3351788-9-maz@kernel.org> <20250930104552.GB1093338@e124191.cambridge.arm.com> 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/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: joey.gouly@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, suzuki.poulose@arm.com, oliver.upton@linux.dev, yuzenghui@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Tue, 30 Sep 2025 11:45:52 +0100, Joey Gouly wrote: > > Observation below > > | > v > > On Mon, Sep 29, 2025 at 05:04:52PM +0100, Marc Zyngier wrote: > > Moving the counter registers is a bit more involved than for the control > > and comparator (there is no shadow data for the counter), but still > > pretty manageable. > > > > Signed-off-by: Marc Zyngier > > --- > > arch/arm64/kvm/guest.c | 7 ------- > > arch/arm64/kvm/sys_regs.c | 34 +++++++++++++++++++++++++++++++--- > > 2 files changed, 31 insertions(+), 10 deletions(-) > > > > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c > > index c23ec9be4ce27..138e5e2dc10c8 100644 > > --- a/arch/arm64/kvm/guest.c > > +++ b/arch/arm64/kvm/guest.c > > @@ -592,19 +592,12 @@ static unsigned long num_core_regs(const struct kvm_vcpu *vcpu) > > } > > > > static const u64 timer_reg_list[] = { > > - KVM_REG_ARM_TIMER_CNT, > > - KVM_REG_ARM_PTIMER_CNT, > > }; > > > > #define NUM_TIMER_REGS ARRAY_SIZE(timer_reg_list) > > > > static bool is_timer_reg(u64 index) > > { > > - switch (index) { > > - case KVM_REG_ARM_TIMER_CNT: > > - case KVM_REG_ARM_PTIMER_CNT: > > - return true; > > - } > > return false; > > } > > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > index 68e88d5c0dfb5..e67eb39ddc118 100644 > > --- a/arch/arm64/kvm/sys_regs.c > > +++ b/arch/arm64/kvm/sys_regs.c > > @@ -1605,12 +1605,38 @@ static int arch_timer_set_user(struct kvm_vcpu *vcpu, > > case SYS_CNTHP_CTL_EL2: > > val &= ~ARCH_TIMER_CTRL_IT_STAT; > > break; > > + case SYS_CNTVCT_EL0: > > + if (!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &vcpu->kvm->arch.flags)) > > + timer_set_offset(vcpu_vtimer(vcpu), kvm_phys_timer_read() - val); > > + return 0; > > + case SYS_CNTPCT_EL0: > > + if (!test_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &vcpu->kvm->arch.flags)) > > + timer_set_offset(vcpu_ptimer(vcpu), kvm_phys_timer_read() - val); > > + return 0; > > } > > > > __vcpu_assign_sys_reg(vcpu, rd->reg, val); > > return 0; > > } > > > > +static int arch_timer_get_user(struct kvm_vcpu *vcpu, > > + const struct sys_reg_desc *rd, > > + u64 *val) > > +{ > > + switch (reg_to_encoding(rd)) { > > + case SYS_CNTVCT_EL0: > > + *val = kvm_phys_timer_read() - timer_get_offset(vcpu_vtimer(vcpu)); > > + break; > > + case SYS_CNTPCT_EL0: > > + *val = kvm_phys_timer_read() - timer_get_offset(vcpu_ptimer(vcpu)); > > + break; > > + default: > > + *val = __vcpu_sys_reg(vcpu, rd->reg); > > Unsure if this is actually an issue but for the _CTL registers, via > access_arch_timer() (kvm_arm_timer_read_sysreg() -> .. -> read_timer_ctl()), > the ARCH_TIMER_CTRL_IT_STAT bit will be set if the timer expired, but that's > not done here. Indeed, but I don't think this really matters, at least not for save/restore. We always clear the ISTATUS bit on restore, and snapshoting CTL is always a racy process. M. -- Without deviation from the norm, progress is not possible.