From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Tue, 31 Mar 2015 17:46:36 +0100 Subject: [PATCH 4/4] arm64: align PHYS_OFFSET to block size In-Reply-To: <20150331161902.GH9119@e104818-lin.cambridge.arm.com> References: <1427125016-3873-5-git-send-email-ard.biesheuvel@linaro.org> <20150325145949.GE26903@localhost> <20150330123011.GB5964@e104818-lin.cambridge.arm.com> <20150330150008.GD5964@e104818-lin.cambridge.arm.com> <20150331144931.GF9119@e104818-lin.cambridge.arm.com> <20150331161902.GH9119@e104818-lin.cambridge.arm.com> Message-ID: <20150331164636.GI9119@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Mar 31, 2015 at 05:19:03PM +0100, Catalin Marinas wrote: > On Tue, Mar 31, 2015 at 03:49:32PM +0100, Catalin Marinas wrote: > > On Mon, Mar 30, 2015 at 08:08:52PM +0200, Ard Biesheuvel wrote: > > > But using early_fixmap() implies using the ordinary page tables > > > manipulation code, which uses __pa/__va > > > So instead, I should refactor those patches to simply pick a VA offset > > > and map the FDT there from head.S > > > > I haven't dug out those patches yet but in principle you should not care > > about __va, just __pa for populating the pmd/pud/pgd. Since with > > fixmap we pre-allocate the page tables in the kernel data section > > (bm_pud/pmd/pte), a __pa implementation that takes KERNEL_PAGE_OFFSET > > into account (as per these patches) is enough, you don't really care > > about the linear PAGE_OFFSET at this stage since you would not provide > > __pa with such virtual address until after setup_machine_fdt(). > > Actually, that's wrong, early_fixmap_init() uses pud/pmd_offset which in > turn use the pmd_offset etc. and pmd_page_vaddr. These would not be > mapped in the linear mapping at this stage. create_mapping() also uses > the *_offset() functions, so we have the same issue. > > So I think we still need to calculate the default initial PHYS_OFFSET in > head.S as we currently do, based on the kernel load address so that > __va() returns a mapping in the initial KERNEL_PAGE_OFFSET range. During > our own early_init_dt_add_memory_arch(), we calculate the real > PHYS_OFFSET but don't set it yet. We should defer the setting of the > real PHYS_OFFSET until we map the first block of memory via > create_mapping(). We know that we can't cope with allocations before the > first block anyway, so this approach may work. Some more brainstorming with Mark, I think we can set the real PHYS_OFFSET immediately after we map the kernel text into the linear mapping (and before mapping the RAM with create_mapping) so that we have access to swapper_pg_dir via this mapping. But we need the initial swapper be pre-populated with pud/pmd for (1) the kernel text at KERNEL_PAGE_OFFSET, (2) kernel text in the linear mapping and (3) the 1st GB of PAGE_OFFSET (to avoid memblock allocations until we mapped some RAM). This way we avoid mandating that the kernel image is only loaded in the first GB of RAM. -- Catalin