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[176.58.241.75]) by smtp.gmail.com with ESMTPSA id m30-20020a17090677de00b00779cde476e4sm2627061ejn.62.2022.10.08.04.08.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 08 Oct 2022 04:08:26 -0700 (PDT) Message-ID: <6e33b687-8862-d208-a707-77a95c61525e@gmail.com> Date: Sat, 8 Oct 2022 14:08:25 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] xen/virtio: Handle cases when page offset > PAGE_SIZE properly Content-Language: en-US To: Oleksandr Tyshchenko , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Cc: Oleksandr Tyshchenko , Stefano Stabellini , Juergen Gross References: <20221007132736.2275574-1-olekstysh@gmail.com> From: Xenia Ragiadakou In-Reply-To: <20221007132736.2275574-1-olekstysh@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/7/22 16:27, Oleksandr Tyshchenko wrote: Hi Oleksandr > From: Oleksandr Tyshchenko > > Passed to xen_grant_dma_map_page() offset in the page > can be > PAGE_SIZE even if the guest uses the same page granularity > as Xen (4KB). > > Before current patch, if such case happened we ended up providing > grants for the whole region in xen_grant_dma_map_page() which > was really unnecessary. The more, we ended up not releasing all > grants which represented that region in xen_grant_dma_unmap_page(). > > Current patch updates the code to be able to deal with such cases. > > Signed-off-by: Oleksandr Tyshchenko > --- > Cc: Juergen Gross > Cc: Xenia Ragiadakou > > Depens on: > https://lore.kernel.org/xen-devel/20221005174823.1800761-1-olekstysh@gmail.com/ > > Should go in only after that series. > --- > drivers/xen/grant-dma-ops.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c > index c66f56d24013..1385f0e686fe 100644 > --- a/drivers/xen/grant-dma-ops.c > +++ b/drivers/xen/grant-dma-ops.c > @@ -168,7 +168,9 @@ static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page, > unsigned long attrs) > { > struct xen_grant_dma_data *data; > - unsigned int i, n_pages = PFN_UP(offset + size); > + unsigned long dma_offset = offset_in_page(offset), > + gfn_offset = PFN_DOWN(offset); > + unsigned int i, n_pages = PFN_UP(dma_offset + size); IIUC, the above with a later patch will become: dma_offset = xen_offset_in_page(offset) gfn_offset = XEN_PFN_DOWN(offset) n_pages = XEN_PFN_UP(dma_offset + size) > grant_ref_t grant; > dma_addr_t dma_handle; > > @@ -187,10 +189,10 @@ static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page, > > for (i = 0; i < n_pages; i++) { > gnttab_grant_foreign_access_ref(grant + i, data->backend_domid, > - xen_page_to_gfn(page) + i, dir == DMA_TO_DEVICE); > + xen_page_to_gfn(page) + i + gfn_offset, dir == DMA_TO_DEVICE); Here, why the pfn is not calculated before passing it to pfn_to_gfn()? I mean sth like pfn_to_gfn(page_to_xen_pfn(page) + gfn_offset + i) > } > > - dma_handle = grant_to_dma(grant) + offset; > + dma_handle = grant_to_dma(grant) + dma_offset; > > return dma_handle; > } -- Xenia