Messages in this thread Patch in this message | | | Date | Fri, 31 Aug 2018 14:15:19 +0800 | From | Feng Tang <> | Subject | Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for NO_BOOTMEM |
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On Thu, Aug 30, 2018 at 03:25:42PM +0200, Thomas Gleixner wrote:
> And where is the problem? We know that we need the fixmap during early boot > anyway, so allocating the PTE page statically and setting it up early > enough is not really rocket science. No allocator required.
Further check shows the page table for fixmap is already setup in [-12M, -10M], but fixmap's address space breaks the expection under certain kernel config. So here is another fix, please review, thanks!
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From f63e4e5c6166a2f8d13ad3142b7a49b2fd1f8edf Mon Sep 17 00:00:00 2001 From: Feng Tang <feng.tang@intel.com> Date: Fri, 31 Aug 2018 13:48:21 +0800 Subject: [PATCH] x86, mm: Make the real fixmap address consistent
We hit a kernel panic when enabling earlycon for a platform, the call trace is:
panic+0xd2/0x220 __alloc_bootmem+0x31/0x34 spp_getpage+0x60/0x8a fill_pte+0x71/0x130 __set_pte_vaddr+0x1d/0x50 set_pte_vaddr+0x3c/0x60 __native_set_fixmap+0x23/0x30 native_set_fixmap+0x30/0x40 setup_earlycon+0x1e0/0x32f param_setup_earlycon+0x13/0x22 do_early_param+0x5b/0x90 parse_args+0x1f7/0x300 parse_early_options+0x24/0x28 parse_early_param+0x65/0x73 setup_arch+0x31e/0x9f1 start_kernel+0x58/0x44e
This panic happens as the earlycon's fixmap address has no pmd/pte ready, and __set_fixmap will try to allocate memory to setup the page table, and trigger panic due to no memory.
x86 kernel actually prepares the page table for fixmap in head_64.S:
NEXT_PAGE(level2_fixmap_pgt) .fill 506,8,0 .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC /* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */ .fill 5,8,0
and it expects the fixmap address is in [-12M, -10M] range, but current code in fixmap.h will break the expectation when X86_VSYSCALL_EMULATION=n
#ifdef CONFIG_X86_VSYSCALL_EMULATION VSYSCALL_PAGE = (FIXADDR_TOP - VSYSCALL_ADDR) >> PAGE_SHIFT, #endif
So removing the "#ifdef" will make the fixmap address space stable in [-12M, -10M] and fix the issue.
Signed-off-by: Feng Tang <feng.tang@intel.com> --- arch/x86/include/asm/fixmap.h | 2 -- 1 file changed, 2 deletions(-)
diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h index e203169931c7..fcf27171f493 100644 --- a/arch/x86/include/asm/fixmap.h +++ b/arch/x86/include/asm/fixmap.h @@ -67,9 +67,7 @@ enum fixed_addresses { #ifdef CONFIG_X86_32 FIX_HOLE, #else -#ifdef CONFIG_X86_VSYSCALL_EMULATION VSYSCALL_PAGE = (FIXADDR_TOP - VSYSCALL_ADDR) >> PAGE_SHIFT, -#endif #endif FIX_DBGP_BASE, FIX_EARLYCON_MEM_BASE, -- 2.14.1
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