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[34.38.181.8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a8fea7de6sm78783785e9.12.2026.05.04.05.19.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2026 05:19:41 -0700 (PDT) Date: Mon, 4 May 2026 12:19:37 +0000 From: Mostafa Saleh To: Jason Gunthorpe 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, jean-philippe@linaro.org, mark.rutland@arm.com, qperret@google.com, tabba@google.com, vdonnefort@google.com, sebastianene@google.com, keirf@google.com Subject: Re: [PATCH v6 06/25] iommu/io-pgtable-arm: Rework to use the iommu-pages API Message-ID: References: <20260501111928.259252-1-smostafa@google.com> <20260501111928.259252-7-smostafa@google.com> <20260501122424.GA6912@ziepe.ca> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260501122424.GA6912@ziepe.ca> On Fri, May 01, 2026 at 09:24:24AM -0300, Jason Gunthorpe wrote: > On Fri, May 01, 2026 at 11:19:08AM +0000, Mostafa Saleh wrote: > > To prepare for supporting io-pgtable-arm in the pKVM hypervisor, > > we need to abstract away standard kernel allocations, frees, virt/phys > > conversions, and DMA API mapping. > > > > This patch introduces a set of generic wrappers in iommu-pages.h: > > - iommu_alloc_data > > - iommu_free_data > > - iommu_virt_to_phys > > - iommu_phys_to_virt > > - iommu_pages_dma_map > > - iommu_pages_dma_mapping_error > > - iommu_pages_dma_unmap > > Wah? This has nothing to do with iommu pages? This just leaking > everything iommu pages abstracted out :( > > When I said to use iommu-pages, I meant to use the existing API, not a > completely different one. > > From an iommu-pages perspective the issue is this code open codes > dma_map_single()/etc instead of using the API surface > iommu_pages_start_incoherent() > > This is annoying to fix beacuse the external allocator messes it up, > but I think with some #ifdef you can probably fix it up. > > So.. I suggest you update it to use the iommu_pages API, #ifdef out > the allocator so the pkvm pkvm doesn't need to deal with it. Then > compile a special iommu-pages for the pkvm side presenting the same > API. I see, we still need to leave the DMA-API calls for the custom config, as I am not sure if it can use pages not backed by the vmemmap, I pushed that into a separate function so it’s easily compiled out. Without this patch, now it looks like: diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c index 0208e5897c29..1583b9916b09 100644 --- a/drivers/iommu/io-pgtable-arm.c +++ b/drivers/iommu/io-pgtable-arm.c @@ -248,26 +248,15 @@ static dma_addr_t __arm_lpae_dma_addr(void *pages) return (dma_addr_t)virt_to_phys(pages); } -static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp, - struct io_pgtable_cfg *cfg, - void *cookie) +static void *__arm_lpae_cfg_alloc(size_t size, gfp_t gfp, + struct io_pgtable_cfg *cfg, + void *cookie) { struct device *dev = cfg->iommu_dev; - size_t alloc_size; dma_addr_t dma; void *pages; - /* - * For very small starting-level translation tables the HW requires a - * minimum alignment of at least 64 to cover all cases. - */ - alloc_size = max(size, 64); - if (cfg->alloc) - pages = cfg->alloc(cookie, alloc_size, gfp); - else - pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp, - alloc_size); - + pages = cfg->alloc(cookie, size, gfp); if (!pages) return NULL; @@ -289,26 +278,67 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp, out_unmap: dev_err(dev, "Cannot accommodate DMA translation for IOMMU page tables\n"); dma_unmap_single(dev, dma, size, DMA_TO_DEVICE); - out_free: - if (cfg->free) - cfg->free(cookie, pages, size); - else - iommu_free_pages(pages); - + cfg->free(cookie, pages, size); return NULL; } -static void __arm_lpae_free_pages(void *pages, size_t size, - struct io_pgtable_cfg *cfg, - void *cookie) +static void __arm_lpae_cfg_free(void *pages, size_t size, + struct io_pgtable_cfg *cfg, + void *cookie) { if (!cfg->coherent_walk) dma_unmap_single(cfg->iommu_dev, __arm_lpae_dma_addr(pages), size, DMA_TO_DEVICE); - if (cfg->free) - cfg->free(cookie, pages, size); + cfg->free(cookie, pages, size); +} + +static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp, + struct io_pgtable_cfg *cfg, + void *cookie) +{ + struct device *dev = cfg->iommu_dev; + size_t alloc_size; + void *pages; + + /* + * For very small starting-level translation tables the HW requires a + * minimum alignment of at least 64 to cover all cases. + */ + alloc_size = max(size, 64); + if (cfg->alloc) + return __arm_lpae_cfg_alloc(alloc_size, gfp, cfg, cookie); + + pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp, alloc_size); + if (!pages) + return NULL; + + if (!cfg->coherent_walk) { + int ret = iommu_pages_start_incoherent(pages, dev); + + if (ret) { + if (ret == -EOPNOTSUPP) + dev_err(dev, "Cannot accommodate DMA translation for IOMMU page tables\n"); + iommu_free_pages(pages); + return NULL; + } + } + + return pages; +} + +static void __arm_lpae_free_pages(void *pages, size_t size, + struct io_pgtable_cfg *cfg, + void *cookie) +{ + if (cfg->free) { + __arm_lpae_cfg_free(pages, size, cfg, cookie); + return; + } + + if (!cfg->coherent_walk) + iommu_pages_free_incoherent(pages, cfg->iommu_dev); else iommu_free_pages(pages); } Thanks, Mostafa > > You should have a pkvm shim header that provides > kmalloc/kfree/virt_to_phys in the normal way and just #include that in > io-pgtable when doing a pkvm build instead of hacking up all the code. Ok, I can do that in another change, but I believe it's better to change the usage in this file to arm_lpae_*(virt_to_phys...) so it's clear which parts are intended for that. Thanks, Mostafa > > Jason