Messages in this thread | | | Date | Tue, 14 May 2013 14:10:54 +0800 | From | Zhang Yanfei <> | Subject | Re: [PATCH] x86, 64bit: Fix a possible bug in switchover in head_64.S |
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于 2013年05月14日 13:51, Yinghai Lu 写道: > On Mon, May 13, 2013 at 5:37 AM, Zhang Yanfei <zhangyanfei.yes@gmail.com> wrote: >> From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> > >> It seems line 119 has a potential bug there. For example, >> the kernel is loaded at physical address 511G+1008M, that is >> 000000000 111111111 111111000 000000000000000000000 >> and the kernel _end is 512G+2M, that is >> 000000001 000000000 000000001 000000000000000000000 >> So in this example, when using the 2nd page to setup PUD (line 114~119), >> rax is 511. >> In line 118, we put rdx which is the address of the PMD page (the 3rd page) >> into entry 511 of the PUD table. But in line 119, the entry we calculate from >> (4096+8)(%rbx,%rax,8) has exceeded the PUD page. IMO, the entry in line >> 119 should be wraparound into entry 0 of the PUD table. >> >> Sorry for not having a machine with memory exceeding 512GB, so I cannot >> test to see if my guess is right or not. Please correct me if I am wrong. >> >> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> >> --- >> arch/x86/kernel/head_64.S | 7 ++++++- >> 1 files changed, 6 insertions(+), 1 deletions(-) >> >> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S >> index 08f7e80..2395d8f 100644 >> --- a/arch/x86/kernel/head_64.S >> +++ b/arch/x86/kernel/head_64.S >> @@ -116,8 +116,13 @@ startup_64: >> shrq $PUD_SHIFT, %rax >> andl $(PTRS_PER_PUD-1), %eax >> movq %rdx, (4096+0)(%rbx,%rax,8) >> + cmp $511, %rax >> + je 1f >> movq %rdx, (4096+8)(%rbx,%rax,8) >> - >> + jmp 2f >> +1: >> + movq %rdx, (4096)(%rbx) >> +2: >> addq $8192, %rbx >> movq %rdi, %rax >> shrq $PMD_SHIFT, %rdi > > yes, that is problem. > > I did test the code cross before for cross 1T and 2T. > maybe we do not access the code during switch... >
Yes, maybe.
> change could be more simple and avoid jmps. > > please check attached, and it does not use jmp
Yeah, this is really simpler.
> > index 08f7e80..321d65e 100644 > --- a/arch/x86/kernel/head_64.S > +++ b/arch/x86/kernel/head_64.S > @@ -115,8 +115,10 @@ startup_64: > movq %rdi, %rax > shrq $PUD_SHIFT, %rax > andl $(PTRS_PER_PUD-1), %eax > - movq %rdx, (4096+0)(%rbx,%rax,8) > - movq %rdx, (4096+8)(%rbx,%rax,8) > + movq %rdx, 4096(%rbx,%rax,8) > + incl %eax > + andl $(PTRS_PER_PUD-1), %eax > + movq %rdx, 4096(%rbx,%rax,8) > > addq $8192, %rbx > movq %rdi, %rax > > And we need cc to stable.
OK, I will send v2 and cc to stable.
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