[+x86 maintainers ...] On Wed, 20 Jul 2022 at 01:22, Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > On 7/19/22 16:13, Andrew Morton wrote: > > On Mon, 18 Jul 2022 16:26:25 +0200 Marco Elver <elver@xxxxxxxxxx> wrote: > > > >> On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > >> [...] > >>>> - This patch has been accused of crashing the kernel: > >>>> > >>>> https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020 > >>>> > >>>> Do we think that report is bogus? > >>> I think all of this is highly architecture-specific... > >> The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g. > >> mm/memblock.c:memblock_free() is also guilty of using __pa() on > >> previously memblock_alloc()'d addresses. Looking at the phys addr > >> before memblock_alloc() does virt_to_phys(), the result of __pa() > >> looks correct even on PAE, at least for the purpose of passing it on > >> to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() != > >> phys_addr) is supposed to tell us here. > >> > > It's only been nine years, so I'm sure Dave can remember why he added > > it ;) > > > > BUG_ON(slow_virt_to_phys((void *)x) != phys_addr); > > > > in arch/x86/mm/physaddr.c:__phys_addr(). > > I think I intended it to double check that the linear map is *actually* > a linear map for 'x'. Sure, we can use the "x - PAGE_OFFSET" shortcut, > but did it turn out to be actually accurate for the address it was handed? > > I'd be curious what the page tables actually say for the address that's > causing problems. test robot just reminded us again: https://lore.kernel.org/all/YufXncrWhJZH0ifB@xsang-OptiPlex-9020/T/#u Few things I noticed: * mm/memblock.c's memblock_free() also uses __pa() to convert back to physical address. Presumably that's also wrong. What should be used instead? * kmemleak happily converts phys_addr_t to unsigned long everywhere, but with i386 PAE, this will narrow a 64-bit address to a 32-bit address. Is that correct? Does kmemleak need a "depends on 64BIT || !PHYS_ADDR_T_64BIT"?
