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[37.24.206.209]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab7d243bba5sm394894666b.71.2025.02.11.23.38.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Feb 2025 23:38:12 -0800 (PST) Message-ID: Date: Wed, 12 Feb 2025 08:38:11 +0100 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 2/2] xen/swiotlb: don't destroy contiguous region in all cases To: Juergen Gross Cc: Stefano Stabellini , Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Oleksandr Tyshchenko , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, x86@kernel.org, iommu@lists.linux.dev References: <20250211120432.29493-1-jgross@suse.com> <20250211120432.29493-3-jgross@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <20250211120432.29493-3-jgross@suse.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11.02.2025 13:04, Juergen Gross wrote: > In case xen_swiotlb_alloc_coherent() needed to create a contiguous > region only for other reason than the memory not being compliant with > the device's DMA mask, there is no reason why this contiguous region > should be destroyed by xen_swiotlb_free_coherent() later. Destroying > this region should be done only, if the memory of the region was > allocated with more stringent placement requirements than the memory > it did replace. I'm not convinced of this: Even the mere property of being contiguous may already be enough to warrant freeing when possible. The hypervisor may not have that many contiguous areas available. The bigger the chunk, the more important to give it back once no longer needed in this shape. Plus also take into account how Xen behaves here: It specifically tries to hold back, during boot, lower addressed memory to later satisfy such requests. Hence even if you don't ask for address restricted memory, you may get back such. You'd need to compare input and output addresses, not input addresses and requested restriction to alleviate this. > --- a/arch/x86/xen/mmu_pv.c > +++ b/arch/x86/xen/mmu_pv.c > @@ -2208,19 +2208,22 @@ void __init xen_init_mmu_ops(void) > static unsigned long discontig_frames[1< > #define VOID_PTE (mfn_pte(0, __pgprot(0))) > -static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order, > - unsigned long *in_frames, > - unsigned long *out_frames) > +static int xen_zap_pfn_range(unsigned long vaddr, unsigned int order, > + unsigned long *in_frames, > + unsigned long *out_frames) > { > int i; > + u64 address_bits = 0; First I was inclined to suggest to use paddr_t here, but ... > struct multicall_space mcs; > > xen_mc_batch(); > for (i = 0; i < (1UL< mcs = __xen_mc_entry(0); > > - if (in_frames) > + if (in_frames) { > in_frames[i] = virt_to_mfn((void *)vaddr); > + address_bits |= in_frames[i] << PAGE_SHIFT; ... why do a shift on every loop iteration when you can ... > + } > > MULTI_update_va_mapping(mcs.mc, vaddr, VOID_PTE, 0); > __set_phys_to_machine(virt_to_pfn((void *)vaddr), INVALID_P2M_ENTRY); > @@ -2229,6 +2232,8 @@ static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order, > out_frames[i] = virt_to_pfn((void *)vaddr); > } > xen_mc_issue(0); > + > + return fls64(address_bits); ... simply add in PAGE_SHIFT here, once? > @@ -2321,7 +2326,8 @@ static int xen_exchange_memory(unsigned long extents_in, unsigned int order_in, > > int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order, > unsigned int address_bits, > - dma_addr_t *dma_handle) > + dma_addr_t *dma_handle, > + unsigned int *address_bits_in) > { > unsigned long *in_frames = discontig_frames, out_frame; > unsigned long flags; > @@ -2336,7 +2342,7 @@ int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order, > spin_lock_irqsave(&xen_reservation_lock, flags); > > /* 1. Zap current PTEs, remembering MFNs. */ > - xen_zap_pfn_range(vstart, order, in_frames, NULL); > + *address_bits_in = xen_zap_pfn_range(vstart, order, in_frames, NULL); Nit: Converting plain int to unsigned int, when there's no real reason to do any conversion. Since xen_zap_pfn_range() can't return a negative value for the caller caring about the return value (yet more obviously so with the suggested adjustment, and then true for both callers), the function could easily return unsigned int. Jan