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SubjectRe: [PATCH] [1/8] GBPAGES: Handle kernel near memory hole in clear_kernel_mapping
On Thu, Jan 03, 2008 at 06:26:57PM +0100, Andi Kleen wrote:
>
> This was a long standing obscure problem in the relocatable kernel. The
> AMD GART driver needs to unmap part of the GART in the kernel direct mapping to
> prevent cache corruption. With the relocatable kernel it is in theory possible
> that the separate kernel text mapping straddles that area too.
>
> Normally it should not happen because GART tends to be >= 2GB, and the kernel
> is normally not loaded that high, but it is possible in theory.
>
> Teach clear_kernel_mapping() about this case.
>
> This will become more important once the kernel mapping uses 1GB pages.
>
> Cc: ebiederm@xmission.com
> Cc: vgoyal@redhat.com
>
> Signed-off-by: Andi Kleen <ak@suse.de>
>
> ---
> arch/x86/mm/init_64.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> Index: linux/arch/x86/mm/init_64.c
> ===================================================================
> --- linux.orig/arch/x86/mm/init_64.c
> +++ linux/arch/x86/mm/init_64.c
> @@ -411,7 +411,8 @@ void __init paging_init(void)
> from the CPU leading to inconsistent cache lines. address and size
> must be aligned to 2MB boundaries.
> Does nothing when the mapping doesn't exist. */
> -void __init clear_kernel_mapping(unsigned long address, unsigned long size)
> +static void __init
> +__clear_kernel_mapping(unsigned long address, unsigned long size)
> {
> unsigned long end = address + size;
>
> @@ -441,6 +442,23 @@ void __init clear_kernel_mapping(unsigne
> __flush_tlb_all();
> }
>
> +#define overlaps(as,ae,bs,be) ((ae) >= (bs) && (as) <= (be))
> +
> +void __init clear_kernel_mapping(unsigned long address, unsigned long size)
> +{
> + int sh = PMD_SHIFT;
> + unsigned long kernel = __pa(__START_KERNEL_map);
> +
> + if (overlaps(kernel>>sh, (kernel + KERNEL_TEXT_SIZE)>>sh,
> + __pa(address)>>sh, __pa(address + size)>>sh)) {
> + printk(KERN_INFO
> + "Kernel at %lx overlaps memory hole at %lx-%lx\n",
> + kernel, __pa(address), __pa(address+size));
> + __clear_kernel_mapping(__START_KERNEL_map+__pa(address), size);

Hi Andi,

Got a question. How will kernel continue to run if we unmap the kernel
text/data region mappings?

Thanks
Vivek


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