Hi Thomas, On Fri, Aug 31, 2018 at 09:36:59PM +0800, Feng Tang wrote: > 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:
Could you review this patch, as at this time window there is no usable memory block or other memory allocators that I know, so I follow the exisitng static fixmap page table code and add one more. Thanks, Feng > > --- > 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 >
