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.t...@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.t...@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
