On 23/08/2024 14:38, Will Deacon wrote: > On Thu, Aug 22, 2024 at 02:28:03AM -0700, Breno Leitao wrote: >> On Mon, Jun 24, 2024 at 12:36:14PM +0100, Will Deacon wrote: >>> On Tue, Jun 18, 2024 at 12:36:03PM +0100, Mark Rutland wrote: >>>> On Tue, Jun 18, 2024 at 01:49:22AM -0700, Breno Leitao wrote: >> >>>>> Since __pa() is a macro to __virt_to_phys(): >>>>> >>>>> #define __pa(x) __virt_to_phys((unsigned long)(x)) >>>>> >>>>> I am curious why this address is special that makes __virt_to_phys() >>>>> unhappy. >>>> >>>> It's a fixmap address rather than a linear-map address. Confusingly >>>> 'virt' generally means the linear map rather than any virtual address, >>>> and usually virt_to_*() only work on linear map addresses. >>>> >>>> I'm not sure how to fix this; the major reason we fixmap the FDT is so >>>> that it can be anywhere in memory (and e.g. may not be in the linear map >>>> at all), so we can't always generate a linear map VA. >>>> >>>> We could stash the PA at boot time, and pass this as an argument to >>>> of_kexec_alloc_and_setup_fdt(). >>> >>> Yeah, if it was passed as an additional argument to early_init_dt_scan(), >>> then the core could could track it. Alternatively, we'd need a helper >>> macro to get the PA and have an arm64-variant for the fixmap (everybody >>> else could use __pa()). >>> >>>> Rob, any thoughts? I couldn't see a neat way of doing this, but maybe we >>>> could initialise an initial_boot_params_phys at setup time, with a bit >>>> of churn to early_init_dt_verify() and friends? >>> >>> Rob? >> >> Hello, is there anything I can do or test to have this moving? > > I've not seen anything from Rob, so the best bet is probably to see if > you can hack up a patch to fix it yourself and then cc the rest of us > when you post it. > > Will > Hi, We are seeing this while doing kexec, so I sent a potential fix in [1]. I did print the values and they are different initial_boot_params_pa 0x6937a00000 __pa(initial_boot_params) 0x8000125e0000 so I think a fix is necessary as we are deleting some random memory while doing kexec which could lead to very difficult to debug crashes if its something critical. I just stashed the physical address and used it later during kexec. I dont see anything that could convert fixmap to phys, but maybe its there and I didn't find it? The other option is to write fix_to_phys which would look something very similar to like kernel_page_present [2]? I do think the patch in [1] is much simpler, but happy to try something like [2] or anything else that is recommended. Thanks! Usama [1] https://lore.kernel.org/all/20241003113840.2972416-1-usamaarif642@xxxxxxxxx/ [2] https://elixir.bootlin.com/linux/v6.11.1/source/arch/arm64/mm/pageattr.c#L213 > _______________________________________________ > kexec mailing list > kexec@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/kexec
