On Fri, Aug 31, 2018 at 01:33:05PM +0200, Thomas Gleixner wrote:
> On Fri, 31 Aug 2018, Feng Tang wrote:
> > On Thu, Aug 30, 2018 at 03:25:42PM +0200, Thomas Gleixner wrote:
> > 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.
>
> Why on earth are you not fixing the damned PTE setup which is the obvious
> and correct thing to do?
Any sugestion? I can only have patch like this:
---
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 15ebc2fc166e..8cdb27ccc3a3 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -446,11 +446,15 @@ NEXT_PAGE(level2_kernel_pgt)
NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
- .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
+ .quad level1_fixmap_pgt0 - __START_KERNEL_map + _PAGE_TABLE_NOENC
+ .quad level1_fixmap_pgt1 - __START_KERNEL_map + _PAGE_TABLE_NOENC
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
- .fill 5,8,0
+ .fill 4,8,0
-NEXT_PAGE(level1_fixmap_pgt)
+NEXT_PAGE(level1_fixmap_pgt0)
+ .fill 512,8,0
+
+NEXT_PAGE(level1_fixmap_pgt1)
.fill 512,8,0
#undef PMDS
Thanks,
Feng
