Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y - Kernel

This is a discussion on Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y - Kernel ; On 10/01/2008 12:47 PM, Vegard Nossum wrote: > Hi, > > Fix for tip/x86/mm-debug (commit 59ea746337c69f6a5f1bc4d5e8544b3cbf12f801). > I'm not sure if choice of names/structure is entirely correct, comments are > appreciated. > From 01613a1949de51c7ab9d0acaaa9a5444722a5cfa Mon Sep 17 00:00:00 2001 > ...

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Thread: Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y

  1. Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y

    On 10/01/2008 12:47 PM, Vegard Nossum wrote:
    > Hi,
    >
    > Fix for tip/x86/mm-debug (commit 59ea746337c69f6a5f1bc4d5e8544b3cbf12f801).
    > I'm not sure if choice of names/structure is entirely correct, comments are
    > appreciated.



    > From 01613a1949de51c7ab9d0acaaa9a5444722a5cfa Mon Sep 17 00:00:00 2001
    > From: Vegard Nossum
    > Date: Wed, 1 Oct 2008 12:36:34 +0200
    > Subject: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y
    >
    > virt_addr_valid() calls __pa(), which calls __phys_addr(). With
    > CONFIG_DEBUG_VIRTUAL=y, __phys_addr() will kill the kernel if the
    > address *isn't* valid. That's clearly wrong for virt_addr_valid().
    >
    > Cc: Jiri Slaby
    > Cc: Andi Kleen
    > Signed-off-by: Vegard Nossum
    > ---
    > diff --git a/arch/x86/kernel/doublefault_32.c b/arch/x86/kernel/doublefault_32.c
    > index 395acb1..1580e0b 100644
    > --- a/arch/x86/kernel/doublefault_32.c
    > +++ b/arch/x86/kernel/doublefault_32.c
    > @@ -66,6 +66,6 @@ struct tss_struct doublefault_tss __cacheline_aligned = {
    > .ds = __USER_DS,
    > .fs = __KERNEL_PERCPU,
    >
    > - .__cr3 = __phys_addr_const((unsigned long)swapper_pg_dir)
    > + .__cr3 = __phys_addr_nodebug((unsigned long)swapper_pg_dir)


    Now, this may be switched back to __pa: __pa_nodebug(swapper_pg_dir);

    > }
    > };

    [...]
    > --- a/include/asm-x86/page_64.h
    > +++ b/include/asm-x86/page_64.h
    > @@ -69,6 +69,7 @@ extern unsigned long max_pfn;
    > extern unsigned long phys_base;
    >
    > extern unsigned long __phys_addr(unsigned long);
    > +#define __phys_addr_nodebug(x) __phys_addr(x)
    > #define __phys_reloc_hide(x) (x)


    x86_64 is screwed in the same way, isn't it?
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  2. Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y

    Ah, and thanks for spotting this!

    On 10/01/2008 01:06 PM, Jiri Slaby wrote:
    > On 10/01/2008 12:47 PM, Vegard Nossum wrote:
    >> Subject: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y


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  3. Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y

    On Wed, Oct 1, 2008 at 1:06 PM, Jiri Slaby wrote:
    > On 10/01/2008 12:47 PM, Vegard Nossum wrote:
    >> Hi,
    >>
    >> Fix for tip/x86/mm-debug (commit 59ea746337c69f6a5f1bc4d5e8544b3cbf12f801).
    >> I'm not sure if choice of names/structure is entirely correct, comments are
    >> appreciated.

    >
    >
    >> From 01613a1949de51c7ab9d0acaaa9a5444722a5cfa Mon Sep 17 00:00:00 2001
    >> From: Vegard Nossum
    >> Date: Wed, 1 Oct 2008 12:36:34 +0200
    >> Subject: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y
    >>
    >> virt_addr_valid() calls __pa(), which calls __phys_addr(). With
    >> CONFIG_DEBUG_VIRTUAL=y, __phys_addr() will kill the kernel if the
    >> address *isn't* valid. That's clearly wrong for virt_addr_valid().
    >>


    ....

    >> --- a/include/asm-x86/page_64.h
    >> +++ b/include/asm-x86/page_64.h
    >> @@ -69,6 +69,7 @@ extern unsigned long max_pfn;
    >> extern unsigned long phys_base;
    >>
    >> extern unsigned long __phys_addr(unsigned long);
    >> +#define __phys_addr_nodebug(x) __phys_addr(x)
    >> #define __phys_reloc_hide(x) (x)

    >
    > x86_64 is screwed in the same way, isn't it?


    Hm. I didn't see any #ifdef CONFIG_DEBUG_VIRTUAL in the x86_64 code,
    so I assumed it wasn't. But it seems that you are right (because the
    checks, or at least some kind of checks, are _always_ performed on
    x86_64 regardless of the CONFIG_DEBUG_VIRTUAL setting). Why doesn't
    the checking in x86_64 code depend on DEBUG_VIRTUAL?

    I will try to make another patch, thanks.


    Vegard

    --
    "The animistic metaphor of the bug that maliciously sneaked in while
    the programmer was not looking is intellectually dishonest as it
    disguises that the error is the programmer's own creation."
    -- E. W. Dijkstra, EWD1036
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