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AJvYcCViHCMRia2wNUauaBpSNHn5XWLrg3MZ9w56Y7tGM82y9EHWJfspflbiBh8iDdPhY5EjfzeSDaY2xSG1euM=@vger.kernel.org X-Gm-Message-State: AOJu0Yxf5nkgmlzpgDhlDc37yncYvFs6RrcIMgxSPdHn3mgKDWB0UxJN EE0qOl9+fOBuTH0V2T8qzN+WrJkSJujFEC0d5k80wAIRk9ibQuj2aH7wa6RTUg== X-Google-Smtp-Source: AGHT+IGEE+x4myqxVpsG+4wlTw+uLRt/VgS3sL49Fo+T3MUgbxgZNUqjr+4TTGSrsMaNaZ7JrXeu3w== X-Received: by 2002:a17:907:d3cf:b0:a86:8285:24a0 with SMTP id a640c23a62f3a-a9029434c42mr1485582266b.23.1726469985553; Sun, 15 Sep 2024 23:59:45 -0700 (PDT) Received: from [172.31.47.100] ([193.118.249.27]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a90610f4375sm272050366b.73.2024.09.15.23.59.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 15 Sep 2024 23:59:45 -0700 (PDT) Message-ID: Date: Mon, 16 Sep 2024 08:59:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] xen/swiotlb: add alignment check for dma buffers To: Juergen Gross Cc: Stefano Stabellini , Oleksandr Tyshchenko , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev References: <20240916064748.18071-1-jgross@suse.com> <20240916064748.18071-2-jgross@suse.com> Content-Language: en-US From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 16.09.2024 08:56, Juergen Gross wrote: > On 16.09.24 08:50, Jan Beulich wrote: >> On 16.09.2024 08:47, Juergen Gross wrote: >>> --- a/drivers/xen/swiotlb-xen.c >>> +++ b/drivers/xen/swiotlb-xen.c >>> @@ -78,9 +78,15 @@ static inline int range_straddles_page_boundary(phys_addr_t p, size_t size) >>> { >>> unsigned long next_bfn, xen_pfn = XEN_PFN_DOWN(p); >>> unsigned int i, nr_pages = XEN_PFN_UP(xen_offset_in_page(p) + size); >>> + phys_addr_t algn = 1ULL << (get_order(size) + PAGE_SHIFT); >>> >>> next_bfn = pfn_to_bfn(xen_pfn); >>> >>> + /* If buffer is physically aligned, ensure DMA alignment. */ >>> + if (IS_ALIGNED(p, algn) && >>> + !IS_ALIGNED(next_bfn << XEN_PAGE_SHIFT, algn)) >> >> And this shift is not at risk of losing bits on Arm LPAE? > > For alignment check this just doesn't matter (assuming XEN_PAGE_SIZE is > smaller than 4G). Oh, yes - of course. A (hypothetical?) strict no-overflow checking mode of the kernel may take issue though, so maybe better to right- shift "algn"? Jan