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[2003:cb:c707:3000:a06b:56f1:d152:db83]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab772f4870bsm134060366b.32.2025.02.06.10.02.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Feb 2025 10:02:19 -0800 (PST) Message-ID: <38333d54-62e4-4d61-a49d-48489d6f977e@redhat.com> Date: Thu, 6 Feb 2025 19:02:17 +0100 Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/6] rust: page: Support borrowing `struct page` and physaddr conversion To: Asahi Lina , Jason Gunthorpe Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Jann Horn , Matthew Wilcox , Paolo Bonzini , Danilo Krummrich , Wedson Almeida Filho , Valentin Obst , Andrew Morton , linux-mm@kvack.org, airlied@redhat.com, Abdiel Janulgue , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, asahi@lists.linux.dev References: <20250202-rust-page-v1-0-e3170d7fe55e@asahilina.net> <1eaf66ba-b2d3-448f-938b-913f17ca98a4@redhat.com> <20250204183933.GJ2296753@ziepe.ca> <1d379007-97c3-4bb9-93da-1a828f955fc4@redhat.com> <20250204202656.GL2296753@ziepe.ca> <08ce9562-9ded-4d95-a495-b60f90d75490@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 04.02.25 22:18, Asahi Lina wrote: > > > On 2/5/25 5:47 AM, David Hildenbrand wrote: >> On 04.02.25 21:41, David Hildenbrand wrote: >>> On 04.02.25 21:26, Jason Gunthorpe wrote: >>>> On Tue, Feb 04, 2025 at 09:05:47PM +0100, David Hildenbrand wrote: >>>>> Fully agreed, this is going into the right direction. Dumping what's >>>>> mapped >>>>> is a different story. Maybe that dumping logic could simply be >>>>> written in C >>>>> for the time being? >>>> >>>> ? >>>> >>>> Isn't dumping just a >>>>     decode pte -> phys_to_virt() -> for_each_u64(virt) -> printk? >>>> >>> >>> IIUC, the problematic bit is that you might not have a directmap such >>> that phys_to_virt() would tell you the whole story. >> >> ... but it's late and I am confused. For dumping the *page table* that >> would not be required, only when dumping mapped page content (and at >> this point I am not sure if that is a requirement). >> >> So hopefully Asahi Lina can clarify what the issue was (if there is >> any :) ). > > Yes, the crash dumper has to dump the mapped page content. In fact, I > don't care about the page tables themselves other than PTE permission > bits, and the page tables alone are not useful for debugging firmware > crashes (and aren't even included in the dump verbatim, at least not the > kernel-allocated ones). The goal of the crash dumper is to take a > complete dump of firmware virtual memory address space (which includes > the kinds of memory I mentioned in [1]). The output is an ELF format > core dump with all memory that the GPU firmware can access, that the > kernel was able to successfully dump (which should be everything except > for MMIO if the bootloader/DT have the right reserved-memory setup). > > I *think* phys_to_virt should work just fine for *this* specific use > case on this platform, but I'm not entirely sure. I still want to use > the various pfn check functions before doing that, to exclude ranges > that would definitely not work. See my other mail, in /proc/kcore we do exactly that. See fs/proc/kcore.c, especially the KCORE_RAM case in read_kcore_iter(). So I would hope that at least for the Devcoredump we can find an alternative that does not require rust bindings, and maybe not even new c code at all (in a perfect world where you could just reuse /proc/kcore). -- Cheers, David / dhildenb