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Tue, 05 Dec 2023 17:01:29 +0000 Date: Tue, 05 Dec 2023 17:01:28 +0000 Message-ID: <86bkb4bn2v.wl-maz@kernel.org> From: Marc Zyngier To: Jason Gunthorpe Cc: Catalin Marinas , ankita@nvidia.com, Shameerali Kolothum Thodi , oliver.upton@linux.dev, suzuki.poulose@arm.com, yuzenghui@huawei.com, will@kernel.org, ardb@kernel.org, akpm@linux-foundation.org, gshan@redhat.com, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, mochs@nvidia.com, kvmarm@lists.linux.dev, kvm@vger.kernel.org, lpieralisi@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory In-Reply-To: <20231205164318.GG2692119@nvidia.com> References: <20231205033015.10044-1-ankita@nvidia.com> <86fs0hatt3.wl-maz@kernel.org> <20231205130517.GD2692119@nvidia.com> <20231205164318.GG2692119@nvidia.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/29.1 (aarch64-unknown-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: jgg@nvidia.com, catalin.marinas@arm.com, ankita@nvidia.com, shameerali.kolothum.thodi@huawei.com, oliver.upton@linux.dev, suzuki.poulose@arm.com, yuzenghui@huawei.com, will@kernel.org, ardb@kernel.org, akpm@linux-foundation.org, gshan@redhat.com, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, mochs@nvidia.com, kvmarm@lists.linux.dev, kvm@vger.kernel.org, lpieralisi@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org 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-20231205_090135_134318_74A42622 X-CRM114-Status: GOOD ( 23.96 ) 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 Tue, 05 Dec 2023 16:43:18 +0000, Jason Gunthorpe wrote: > > On Tue, Dec 05, 2023 at 04:22:33PM +0000, Catalin Marinas wrote: > > That's an argument to restrict this feature to PCIe. It's really about > > fewer arguments on the behaviour of other devices. Marc did raise > > another issue with the GIC VCPU interface (does this even have a vma in > > the host VMM?). That's a class of devices where the mapping is > > context-switched, so the TLBI+DSB rules don't help. There is no vma. The CPU interface is entirely under control of KVM. Userspace only provides the IPA for the mapping. > > I don't know anything about the GIC VCPU interface, to give any > comment unfortunately. Since it seems there is something to fix here I > would appreciate some background.. > > When you say it is context switched do you mean kvm does a register > write on every vm entry to set the proper HW context for the vCPU? The CPU interface is mapped in every guest S2 page tables as a per-CPU device, and under complete control of the guest. There is no KVM register write to that frame (unless we're proxying it, but that's for another day). > > We are worrying that register write will possibly not order after > NORMAL_NC? Guest maps the device as Normal-NC (because it now can), which means that there is no control over the alignment or anything like that. The accesses could also be reordered, and/or hit after a context switch to another guest. Which is why KVM has so far used nGnRE as the mapping type. 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