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([2620:10d:c092:500::7:ca73]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9a91559b33sm487702366b.116.2024.10.23.08.24.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Oct 2024 08:24:23 -0700 (PDT) Message-ID: <237a32b7-e2c9-4db4-9358-918ce54da779@gmail.com> Date: Wed, 23 Oct 2024 16:24:22 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] of/kexec: save pa of initial_boot_params for arm64 and use it at kexec To: Rob Herring Cc: mark.rutland@arm.com, will@kernel.org, leitao@debian.org, catalin.marinas@arm.com, saravanak@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, kexec@lists.infradead.org References: <20241003113840.2972416-1-usamaarif642@gmail.com> <20241004000316.GA1910499-robh@kernel.org> <4b9456a3-47ea-4a00-92fe-131ccd80e550@gmail.com> <1e117d65-b454-4d5c-b03a-c3ab3b078093@gmail.com> Content-Language: en-US From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 23/10/2024 16:17, Rob Herring wrote: > On Wed, Oct 23, 2024 at 9:43 AM Usama Arif wrote: >> >> >> >> On 23/10/2024 14:40, Rob Herring wrote: >>> On Mon, Oct 7, 2024 at 10:30 AM Usama Arif wrote: >>>> >>>> >>>> >>>> On 07/10/2024 15:39, Rob Herring wrote: >>>>> On Mon, Oct 7, 2024 at 9:06 AM Usama Arif wrote: >>>>>> >>>>>> >>>>>> >>>>>> On 04/10/2024 01:03, Rob Herring wrote: >>>>>>> On Thu, Oct 03, 2024 at 12:38:40PM +0100, Usama Arif wrote: >>>>>>>> __pa() is only intended to be used for linear map addresses and using >>>>>>>> it for initial_boot_params which is in fixmap for arm64 will give an >>>>>>>> incorrect value. Hence stash the physical address when it is known at >>>>>>>> boot time and use it at kexec time instead of converting the virtual >>>>>>>> address using __pa(). >>>>>>>> >>>>>>>> Reported-by: Breno Leitao >>>>>>>> Suggested-by: Mark Rutland >>>>>>>> Signed-off-by: Usama Arif >>>>>>>> Fixes: ac10be5cdbfa ("arm64: Use common of_kexec_alloc_and_setup_fdt()") >>>>>>>> --- >>>>>>>> arch/arm64/kernel/setup.c | 8 ++++++++ >>>>>>>> drivers/of/fdt.c | 6 ++++++ >>>>>>>> drivers/of/kexec.c | 8 ++++++-- >>>>>>>> include/linux/of_fdt.h | 2 ++ >>>>>>>> 4 files changed, 22 insertions(+), 2 deletions(-) >>>>>>>> >>>>>>>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c >>>>>>>> index b22d28ec8028..a4d96f5e2e05 100644 >>>>>>>> --- a/arch/arm64/kernel/setup.c >>>>>>>> +++ b/arch/arm64/kernel/setup.c >>>>>>>> @@ -194,6 +194,14 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys) >>>>>>>> /* Early fixups are done, map the FDT as read-only now */ >>>>>>>> fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO); >>>>>>>> >>>>>>>> + /* >>>>>>>> + * Save dt_phys address so that it can be used later for kexec. This >>>>>>>> + * is done as __pa() is only intended to be used for linear map addresses >>>>>>>> + * and using it for initial_boot_params which is in fixmap will give an >>>>>>>> + * incorrect value. >>>>>>>> + */ >>>>>>>> + set_initial_boot_params_pa(dt_phys); >>>>>>> >>>>>>> No new arch->dt functions please. If we need to save off the PA, then do >>>>>>> that when we set initial_boot_params. >>>>>>> >>>>>>> Rob >>>>>> >>>>>> >>>>>> initial_boot_params is set in early_init_dt_verify, called by early_init_dt_scan. >>>>>> This is done in setup_machine_fdt in arm64 where the PA is available, >>>>>> but in other functions in other architectures, where the PA is not available. >>>>> >>>>> Doesn't __pa() work for all the other architectures? That's what your >>>>> patch indicates. >>>>> >>>> >>>> Yes, __pa() works for all other architectures. >>>> >>>> But we would need to add initial_boot_params_pa of type phys_addr_t >>>> as an argument for early_init_dt_scan, which is called by all other archs, >>>> and we technically cant use 0 as an invalid value. >>>> >>>> We could convert initial_boot_params_pa to void *, and pass NULL for all >>>> other archs. But again, I don't really think we should be changing the >>>> early_init_dt_scan(dt_virt) call in all other archs to >>>> early_init_dt_scan(dt_virt, NULL) just to save initial_boot_params_pa >>>> in arm64? >>>> >>>>>> So it makes it quite messy to set it in the same place as initial_boot_params. >>>>>> Its only needed for arm64 and making a change in all archs probably isnt a good idea? >>>>>> >>>>>> Any reason to not add a new function to make arch -> of/fdt call? >>>>> >>>>> Yes. It is the opposite direction I have reworked the interfaces to. >>>>> We don't want each arch calling various early DT functions at random >>>>> times and order. That's fragile when the DT functions make assumptions >>>>> about when they are called or what's been initialized already. >>>>> >>>>> Another option is to make arm64 copy the DT as some arches do. >>>>> >>>>> Rob >>>> >>>> Ah maybe I didn't understand this properly, but isnt early_init_dt_scan an >>>> arch -> of/fdt interfaces. set_initial_boot_params_pa is a similar interface >>>> to early_init_dt_scan? >>> >>> Yes, and I don't want more APIs if they can be avoided. When is >>> set_initial_boot_params_pa() supposed to be called? Is it before or >>> after early_init_dt_scan()? >> >> Its only needed in arm64, and can be either before or after, as long as its >> somewhere in setup_machine_fdt, where dt_phys is available. > > Maybe only arm64 today. What happens when riscv decides they too want > to support the DT anywhere in memory including outside the linear > address map and then they need the same thing. > >>> Can subsequent OF functions assume the PA >>> is valid? >> >> After set_initial_boot_params_pa has been called, yes. > > How do I know it has been called? Do I have to go wade thru every arch > to see? You could document the requirement to be immediately after > early_init_dt_scan(), but then how do you enforce that? You can't > unless you design the interface to just avoid the problem in the first > place. > >>> If an arch doesn't call set_initial_boot_params_pa() is >>> __pa() valid or did they just forget to call it? >> >> Only arm64 seems to do the fixmap as discussed in >> https://lore.kernel.org/all/1ea5538f-7e96-4034-9af9-e2d5fd72e069@gmail.com/, >> so __pa should work in others. >> >> Requiring the PA to >>> be set at the same time as initial_boot_params avoids all those issues >>> with any period of time having the PA incorrect. >>> >> >> Are you recommending I send a patch which changes all archs to call >> early_init_dt_scan(dt_virt, NULL)? >> or maybe early_init_dt_scan(dt_virt, __pa(dt_virt))? >> and arm to call early_init_dt_scan(dt_virt, dt_phys). > > I believe that's what I suggested already, so yes. Whether NULL or > __pa(dt_virt))? __pa() would be better because then the arch has to > think about whether that is right or not. Sounds good! Will send a v2 with the change. Thanks > >> Happy to do send a v2 with that if its the way forward, although I feel >> set_initial_boot_params_pa() in just one arch might be better than >> changing this for all archs. > > We don't work around kernel APIs if they don't meet changing needs. We > change them. > > Rob