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Thu, 19 Aug 2021 09:11:16 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mGe4u-007prd-QF for linux-arm-kernel@lists.infradead.org; Thu, 19 Aug 2021 09:11:14 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AA2D06108B; Thu, 19 Aug 2021 09:11:11 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mGe4r-005vyM-No; Thu, 19 Aug 2021 10:11:09 +0100 Date: Thu, 19 Aug 2021 10:11:09 +0100 Message-ID: <874kblsssy.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton , Andrew Jones Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, Paolo Bonzini , Sean Christopherson , Peter Shier , Jim Mattson , David Matlack , Ricardo Koller , Jing Zhang , Raghavendra Rao Anata , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, Will Deacon , Catalin Marinas Subject: Re: [PATCH v7 3/7] KVM: arm64: Allow userspace to configure a vCPU's virtual offset In-Reply-To: <20210816001217.3063400-4-oupton@google.com> References: <20210816001217.3063400-1-oupton@google.com> <20210816001217.3063400-4-oupton@google.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/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: oupton@google.com, drjones@redhat.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, pbonzini@redhat.com, seanjc@google.com, pshier@google.com, jmattson@google.com, dmatlack@google.com, ricarkol@google.com, jingzhangos@google.com, rananta@google.com, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, will@kernel.org, catalin.marinas@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-20210819_021112_931339_DEC6F2F9 X-CRM114-Status: GOOD ( 26.35 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 16 Aug 2021 01:12:13 +0100, Oliver Upton wrote: > > Allow userspace to access the guest's virtual counter-timer offset > through the ONE_REG interface. The value read or written is defined to > be an offset from the guest's physical counter-timer. Add some > documentation to clarify how a VMM should use this and the existing > CNTVCT_EL0. > > Signed-off-by: Oliver Upton > Reviewed-by: Andrew Jones > --- > Documentation/virt/kvm/api.rst | 10 ++++++++++ > arch/arm64/include/uapi/asm/kvm.h | 1 + > arch/arm64/kvm/arch_timer.c | 23 +++++++++++++++++++++++ > arch/arm64/kvm/guest.c | 6 +++++- > include/kvm/arm_arch_timer.h | 1 + > 5 files changed, 40 insertions(+), 1 deletion(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index dae68e68ca23..adb04046a752 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -2463,6 +2463,16 @@ arm64 system registers have the following id bit patterns:: > derived from the register encoding for CNTV_CVAL_EL0. As this is > API, it must remain this way. > > +.. warning:: > + > + The value of KVM_REG_ARM_TIMER_OFFSET is defined as an offset from > + the guest's view of the physical counter-timer. > + > + Userspace should use either KVM_REG_ARM_TIMER_OFFSET or > + KVM_REG_ARM_TIMER_CNT to pause and resume a guest's virtual > + counter-timer. Mixed use of these registers could result in an > + unpredictable guest counter value. > + > arm64 firmware pseudo-registers have the following bit pattern:: > > 0x6030 0000 0014 > diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h > index b3edde68bc3e..949a31bc10f0 100644 > --- a/arch/arm64/include/uapi/asm/kvm.h > +++ b/arch/arm64/include/uapi/asm/kvm.h > @@ -255,6 +255,7 @@ struct kvm_arm_copy_mte_tags { > #define KVM_REG_ARM_TIMER_CTL ARM64_SYS_REG(3, 3, 14, 3, 1) > #define KVM_REG_ARM_TIMER_CVAL ARM64_SYS_REG(3, 3, 14, 0, 2) > #define KVM_REG_ARM_TIMER_CNT ARM64_SYS_REG(3, 3, 14, 3, 2) > +#define KVM_REG_ARM_TIMER_OFFSET ARM64_SYS_REG(3, 4, 14, 0, 3) > Andrew, does this warrant an update to the selftest that checks for sysreg visibility? I am also wondering how a VMM such as QEMU is going to deal with the above restriction, given the way it blindly saves/restores all the registers that KVM exposes, hence hitting that mixed-use that the documentation warns about... Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel