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[142.162.112.119]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c09688e3d4sm3545746985a.13.2026.01.04.16.02.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 04 Jan 2026 16:02:30 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vcY3J-0000000156c-2OeL; Sun, 04 Jan 2026 20:02:29 -0400 Date: Sun, 4 Jan 2026 20:02:29 -0400 From: Jason Gunthorpe To: Dawei Li Cc: will@kernel.org, robin.murphy@arm.com, joro@8bytes.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, set_pte_at@outlook.com, stable@vger.kernel.org Subject: Re: [PATCH] iommu/arm-smmu-v3: Maintain valid access attributes for non-coherent SMMU Message-ID: <20260105000229.GC125261@ziepe.ca> References: <20251229002354.162872-1-dawei.li@linux.dev> <20260102184113.GA125261@ziepe.ca> <20260104133532.GA173992@wendao-VirtualBox> Precedence: bulk X-Mailing-List: iommu@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: <20260104133532.GA173992@wendao-VirtualBox> > > /* DMA for "CMDQ MSI" which targets q->base_dma allocated by arm_smmu_init_one_queue() */ > > > > > @@ -1612,11 +1624,18 @@ void arm_smmu_make_cdtable_ste(struct arm_smmu_ste *target, > > > (cd_table->cdtab_dma & STRTAB_STE_0_S1CTXPTR_MASK) | > > > FIELD_PREP(STRTAB_STE_0_S1CDMAX, cd_table->s1cdmax)); > > > > > > + if (smmu_coherent(smmu)) { > > > + val = FIELD_PREP(STRTAB_STE_1_S1CIR, STRTAB_STE_1_S1C_CACHE_WBRA) | > > > + FIELD_PREP(STRTAB_STE_1_S1COR, STRTAB_STE_1_S1C_CACHE_WBRA) | > > > + FIELD_PREP(STRTAB_STE_1_S1CSH, ARM_SMMU_SH_ISH); > > > + } else { > > > + val = FIELD_PREP(STRTAB_STE_1_S1CIR, STRTAB_STE_1_S1C_CACHE_NC) | > > > + FIELD_PREP(STRTAB_STE_1_S1COR, STRTAB_STE_1_S1C_CACHE_NC) | > > > + FIELD_PREP(STRTAB_STE_1_S1CSH, ARM_SMMU_SH_OSH); > > > + } > > > > This one is "CD fetch" allocated by arm_smmu_alloc_cd_ptr() > > > > etc > > > > And note that the above will need this hunk too: > > > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c > > @@ -432,6 +432,14 @@ size_t arm_smmu_get_viommu_size(struct device *dev, > > !(smmu->features & ARM_SMMU_FEAT_S2FWB)) > > return 0; > > > > + /* > > + * When running non-coherent we can't suppot S2FWB since it will also > > + * force a coherent CD fetch, aside from the question of what > > + * S2FWB/CANWBS even does with non-coherent SMMUs. > > + */ > > + if (!smmu_coherent(smmu)) > > + return 0; > > I was wondering why S2FWB can affect CD fetching before reading 13.8. Yeah, that table is super useful > + if (!fwb) { > + val = FIELD_PREP(STRTAB_STE_1_S1CIR, STRTAB_STE_1_S1C_CACHE_NC) | > + FIELD_PREP(STRTAB_STE_1_S1COR, STRTAB_STE_1_S1C_CACHE_NC) | > + FIELD_PREP(STRTAB_STE_1_S1CSH, ARM_SMMU_SH_OSH); > + } else { > + dev_warn(&smmu->dev, "Inconsitency between COHACC & S2FWB\n"); > + /* FIX ME */ > + return; I prefer we block it as I showed instead of printing a warning, cache inconsistencies in virtualization can become security problems. Though it is probably good to add a comment here about s2fwb also Jason