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Tue, 18 Feb 2025 16:33:29 +0000 Date: Tue, 18 Feb 2025 16:33:26 +0000 Message-ID: <86eczvrz55.wl-maz@kernel.org> From: Marc Zyngier To: Ganapatrao Kulkarni Cc: Eric Auger , Oliver Upton , kvmarm , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, christoffer.dall@arm.com, suzuki.poulose@arm.com, will@kernel.org, catalin.marinas@arm.com, coltonlewis@google.com, joey.gouly@arm.com, yuzenghui@huawei.com, darren@os.amperecomputing.com, vishnu@os.amperecomputing.com Subject: Re: [PATCH] KVM: arm64: nv: Set ISTATUS for emulated timers, If timer expired In-Reply-To: <1a19dacc-72ca-4631-bce8-7426b3de0b47@os.amperecomputing.com> References: <86y10osr19.wl-maz@kernel.org> <4d443db1-85b1-4071-acd5-3187deb9cb17@redhat.com> <2f6b2cb1-3d32-480a-9801-9b993ae74e2d@os.amperecomputing.com> <152d262e-641d-4bb1-9656-a13e049d62c4@redhat.com> <86h661wje4.wl-maz@kernel.org> <4a9fbdd9-ad23-44bc-8ba5-399f08068db4@redhat.com> <86cygpwfy0.wl-maz@kernel.org> <86frkptzr6.wl-maz@kernel.org> <86bjvdtxb5.wl-maz@kernel.org> <8da22249-eedb-477b-98d8-f50dee56f1f7@redhat.com> <87tt8v14j2.wl-maz@kernel.org> <1a19dacc-72ca-4631-bce8-7426b3de0b47@os.amperecomputing.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/29.4 (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: gankulkarni@os.amperecomputing.com, eauger@redhat.com, oliver.upton@linux.dev, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, christoffer.dall@arm.com, suzuki.poulose@arm.com, will@kernel.org, catalin.marinas@arm.com, coltonlewis@google.com, joey.gouly@arm.com, yuzenghui@huawei.com, darren@os.amperecomputing.com, vishnu@os.amperecomputing.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-20250218_083333_346714_838FEF1C X-CRM114-Status: GOOD ( 32.87 ) 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 Tue, 18 Feb 2025 07:33:11 +0000, Ganapatrao Kulkarni wrote: > > > Hi Marc, > > On 15-02-2025 11:20 pm, Marc Zyngier wrote: > > On Mon, 10 Feb 2025 18:26:48 +0000, > > Eric Auger wrote: > >> > >> Hi Marc, > >> > >> On 2/7/25 7:38 PM, Marc Zyngier wrote: > >>> On Fri, 07 Feb 2025 18:09:58 +0000, > >>> Oliver Upton wrote: > >>>> > >>>> Hey, > >>>> > >>>> On Fri, Feb 07, 2025 at 05:45:33PM +0000, Marc Zyngier wrote: > >>>>> I found at least one issue that could fail the migration. Before the > >>>>> VM starts running, we limit the feature set to the subset we actually > >>>>> support with NV. > >>>>> > >>>>> By doing this, we also change the value of IDreg fields that are not > >>>>> writable, because they describe features that we don't support. > >>>>> Obviously, that fails on restore. > >>>>> > >>>>> I need to have a think... > >>>> > >>>> We spoke about this a while ago (and I forgot til now), but I was > >>>> wondering if we could use vCPU feature flags to describe NV, including > >>>> the selection between FEAT_E2H0 and FEAT_VHE. > >>>> > >>>> I think this might match userspace expectations a bit more closely where > >>>> the state of the ID registers after init gives the actual feature set > >>>> supported by the VM. > >>> > >>> I'm not sure that's enough. Let me give you an example: > >>> > >>> My host has FEAT_XNX, described in ID_AA64MMFR1_EL1.XNX. For whatever > >>> reason, we don't allow this field to be written to, even out of NV > >>> context. This is odd, because for an EL1 VM, this field means nothing > >>> at all. > >> So the curprit fields for me look like > >> > >> - ID_AA64MMFR1_EL1.XNX > >> - ID_AA64DFR0_EL1.DoubleLock > >> - ID_AA64PFR0_EL1.RAS > >> > >> This is still based on your nv-next branch from Jan 9 > >> https://github.com/eauger/linux/tree/nv_next_jan9_2025 > > > > I have now pushed out a new nv-next branch with the new and improved > > UAPI. I expect migration to work a bit better, or at least not to > > explode on ID register restore. You will notice that things have > > changed a bit (extra flag and cap for FEAT_E2H0), but nothing really > > major. > > > > Tried nv-next branch and it is breaking(kernel Oops) for normal VM > boot itself with qemu. Looks like this is happening since qemu is > trying to write to ID_UNALLOCATED mapped registers as part of > save-restore of registers. Yeah, ID_UNALLOCATED is in pretty bad shape overall. For start, it doesn't even have a name associated to it, and then everything else falls apart. I'll rework it shortly, thanks for the heads up. M. -- Without deviation from the norm, progress is not possible.