On Tue, Mar 11, 2025 at 05:51:06PM +0000, Mark Brown wrote: > On Thu, Mar 06, 2025 at 08:51:20PM +0200, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx> > > > > high_memory defines upper bound on the directly mapped memory. > > This bound is defined by the beginning of ZONE_HIGHMEM when a system has > > high memory and by the end of memory otherwise. > > > > All this is known to generic memory management initialization code that > > can set high_memory while initializing core mm structures. > > > > Remove per-architecture calculation of high_memory and add a generic > > version to free_area_init(). > > This patch appears to be causing breakage on a number of 32 bit arm > platforms, including qemu's virt-2.11,gic-version=3. Affected platforms > die on boot with no output, a bisect with qemu points at this commit and > those for physical platforms appear to be converging on the same place. I'm not convinced that the old and the new code is doing the same thing. The new code: + phys_addr_t highmem = memblock_end_of_DRAM(); + +#ifdef CONFIG_HIGHMEM + unsigned long pfn = arch_zone_lowest_possible_pfn[ZONE_HIGHMEM]; + + if (arch_has_descending_max_zone_pfns() || highmem > PFN_PHYS(pfn)) + highmem = PFN_PHYS(pfn); +#endif + + high_memory = phys_to_virt(highmem - 1) + 1; First, when CONFIG_HIGHMEM is disabled, this code assumes that the last byte of DRAM declared to memblock is the highmem limit. This _could_ overflow phys_to_virt() and lead to an invalid value for high_memory. Second, arch_zone_lowest_possible_pfn[ZONE_HIGHMEM] is the _start_ of highmem. This is not what arch code sets high_memory to - because the start of highmem may not contiguously follow on from lowmem. In arch/arm/mm/mmu.c, lowmem_limit is computed to be the highest + 1 physical address that lowmem can possibly be, taking into account the amount of vmalloc memory that is required. This is used to set high_memory. We also limit the amount of usable RAM via memblock_set_current_limit() which memblock_end_of_DRAM() doesn't respect. I don't think the proposed generic version is suitable for 32-bit arm. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
