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[34.76.60.220]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-69f34b9b064sm2548716a12.11.2026.07.23.08.15.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2026 08:15:48 -0700 (PDT) Date: Thu, 23 Jul 2026 15:15:42 +0000 From: Mostafa Saleh To: Sebastian Ene Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, iommu@lists.linux.dev, catalin.marinas@arm.com, will@kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, joro@8bytes.org, jgg@ziepe.ca, mark.rutland@arm.com, qperret@google.com, tabba@google.com, vdonnefort@google.com, keirf@google.com Subject: Re: [PATCH v7 14/24] iommu/arm-smmu-v3-kvm: Shadow the command queue Message-ID: References: <20260715115906.2664882-1-smostafa@google.com> <20260715115906.2664882-15-smostafa@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Seb, On Thu, Jul 23, 2026 at 02:55:08PM +0000, Sebastian Ene wrote: > On Wed, Jul 15, 2026 at 11:58:55AM +0000, Mostafa Saleh wrote: > > + * size as the host. > > + * Only populate base_dma and llq.max_n_shift, the hypervisor will init > > + * the rest. > > + */ > > + cmdq_base = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, SMMU_KVM_CMDQ_ORDER); > > + if (!cmdq_base) > > + return -ENOMEM; > > Hi Mostafa, > > Isn't this over-allocating when PAGE_SIZE > 4kB ? Yes, that means the queue have different size depending on PAGE_SIZE, In the kernel driver CMDQ_MAX_SZ_SHIFT is defined in terms of page size also, but I think in the hypervisor it doesn't really matter, I can change this to a fixed size and use alloc_pages_exact(). > > > + > > + smmu->cmdq.base_dma = virt_to_phys(cmdq_base); > > + smmu->cmdq.llq.max_n_shift = SMMU_KVM_CMDQ_ORDER + PAGE_SHIFT - CMDQ_ENT_SZ_SHIFT; > > + > > if (of_dma_is_coherent(dev->of_node)) > > smmu->features |= ARM_SMMU_FEAT_COHERENCY; > > > > diff --git a/drivers/iommu/arm/arm-smmu-v3/pkvm/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/pkvm/arm-smmu-v3.c > > index af06c832fc6f..9f76f4e82341 100644 > > --- a/drivers/iommu/arm/arm-smmu-v3/pkvm/arm-smmu-v3.c > > +++ b/drivers/iommu/arm/arm-smmu-v3/pkvm/arm-smmu-v3.c > > @@ -11,7 +11,6 @@ > > #include > > > > #include "arm_smmu_v3.h" > > -#include "../arm-smmu-v3.h" > > > > size_t __ro_after_init kvm_hyp_arm_smmu_v3_count; > > struct hyp_arm_smmu_v3_device *kvm_hyp_arm_smmu_v3_smmus; > > @@ -21,10 +20,68 @@ struct hyp_arm_smmu_v3_device *kvm_hyp_arm_smmu_v3_smmus; > > (smmu) != &kvm_hyp_arm_smmu_v3_smmus[kvm_hyp_arm_smmu_v3_count]; \ > > (smmu)++) > > > > +#define cmdq_size(cmdq) ((1 << ((cmdq)->llq.max_n_shift)) * CMDQ_ENT_DWORDS * 8) > > + > > +static bool is_cmdq_enabled(struct hyp_arm_smmu_v3_device *smmu) > > +{ > > + return FIELD_GET(CR0_CMDQEN, smmu->cr0); > > +} > > + > > +/* > > + * CMDQ, STE host copies are accessed by the hypervisor, we share them to > > + * - Prevent the host from passing protected VM memory. > > + * - Having them mapped in the hyp page table. > > + */ > > +static int smmu_share_pages(phys_addr_t addr, size_t size) > > +{ > > + size_t nr_pages = PAGE_ALIGN(size + (addr & ~PAGE_MASK)) >> PAGE_SHIFT; > > + phys_addr_t base = addr & PAGE_MASK; > > + int i, ret; > > + > > + for (i = 0 ; i < nr_pages ; ++i) { > > + if (__pkvm_host_share_hyp((base + i * PAGE_SIZE) >> PAGE_SHIFT)) { > > + while (i--) > > + __pkvm_host_unshare_hyp((base + i * PAGE_SIZE) >> PAGE_SHIFT); > > + return -EPERM; > > + } > > + } > > + > > + ret = hyp_pin_shared_mem(hyp_phys_to_virt(base), > > + hyp_phys_to_virt(base + nr_pages * PAGE_SIZE)); > > + if (ret) { > > + for (i = 0 ; i < nr_pages ; ++i) > > + __pkvm_host_unshare_hyp((base + i * PAGE_SIZE) >> PAGE_SHIFT); > > + } > > + > > + return ret; > > +} > > + > > +static int smmu_unshare_pages(phys_addr_t addr, size_t size) > > +{ > > + size_t nr_pages = PAGE_ALIGN(size + (addr & ~PAGE_MASK)) >> PAGE_SHIFT; > > + phys_addr_t base = addr & PAGE_MASK; > > + int i, ret; > > + > > + hyp_unpin_shared_mem(hyp_phys_to_virt(base), > > + hyp_phys_to_virt(base + nr_pages * PAGE_SIZE)); > > + > > + for (i = 0 ; i < nr_pages ; ++i) { > > + ret = __pkvm_host_unshare_hyp((base + i * PAGE_SIZE) >> PAGE_SHIFT); > > + if (ret) > > + return ret; > > + } > > + > > + return 0; > > +} > > + > > /* Put the device in a state that can be probed by the host driver. */ > > static void smmu_deinit_device(struct hyp_arm_smmu_v3_device *smmu) > > { > > WARN_ON(__pkvm_hyp_donate_host_mmio(smmu->mmio_addr, smmu->mmio_size)); > > + > > + if (smmu->cmdq.base) > > + WARN_ON(__pkvm_hyp_donate_host(smmu->cmdq.base_dma >> PAGE_SHIFT, > > + cmdq_size(&smmu->cmdq) >> PAGE_SHIFT)); > > smmu->base = NULL; > > } > > > > @@ -75,6 +132,31 @@ static int smmu_probe(struct hyp_arm_smmu_v3_device *smmu) > > return 0; > > } > > > > +/* > > + * The kernel part of the driver will allocate the shadow cmdq, > > + * and zero it. This function only donates it. > > + */ > > +static int smmu_init_cmdq(struct hyp_arm_smmu_v3_device *smmu) > > +{ > > + size_t cmdq_nr_pages = cmdq_size(&smmu->cmdq) >> PAGE_SHIFT; > > + int ret; > > + > > + ret = __pkvm_host_donate_hyp(smmu->cmdq.base_dma >> PAGE_SHIFT, cmdq_nr_pages); > > + if (ret) > > + return ret; > > + > > + smmu->cmdq.base = hyp_phys_to_virt(smmu->cmdq.base_dma); > > + smmu->cmdq.prod_reg = smmu->base + ARM_SMMU_CMDQ_PROD; > > + smmu->cmdq.cons_reg = smmu->base + ARM_SMMU_CMDQ_CONS; > > + smmu->cmdq.q_base = smmu->cmdq.base_dma | > > + FIELD_PREP(Q_BASE_LOG2SIZE, smmu->cmdq.llq.max_n_shift); > > + smmu->cmdq.ent_dwords = CMDQ_ENT_DWORDS; > > + writel_relaxed(0, smmu->cmdq.prod_reg); > > + writel_relaxed(0, smmu->cmdq.cons_reg); > > + writeq_relaxed(smmu->cmdq.q_base, smmu->base + ARM_SMMU_CMDQ_BASE); > > do we need a dsb here ? I do not think so, why would it be needed? No data written at this point. When commands are written, writel() is used to advance the queue pointer which includes a barrier to enusre that the commands are observed. Thanks, Mostafa > > > Thanks, > Sebastian