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SubjectRe: [PATCH] x86: use pgd accessors when cloning a pgd range.
On Wed, Oct 27, 2010 at 09:50:13AM +0100, Ian Campbell wrote:
> Page tables should always be updated using the proper accessor
> methods. Not doing so bypasses the paravirt infrastructure.
>
> In this case the failure to do so was exposed under Xen by
> b40827fa7268 "x86-32, mm: Add an initial page table for core
> bootstrapping".
>
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: H. Peter Anvin <hpa@linux.intel.com>
> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
> ---
> arch/x86/include/asm/pgtable.h | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index ada823a..0b4c514 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -619,7 +619,10 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm,
> */
> static inline void clone_pgd_range(pgd_t *dst, pgd_t *src, int count)
> {
> - memcpy(dst, src, count * sizeof(pgd_t));
> + int i;
> +
> + for (i=0; i<count; i++)
> + set_pgd(&dst[i], src[i]);

Hmm, this slows down clone_pgd_range(). It is called at 3 sites total,
two of which happen only on boot in setup_arch() so they can be ignored
but the callchain

copy_process()
...
mm_init()
|->mm_alloc_pgd()
|->pgd_alloc()
|->pgd_ctor()
|->clone_pgd_range()

could become noticeable. To be on the safe side, I'd make
clone_pgd_range() a macro calling either the native or the xen version..

hpa?

--
Regards/Gruss,
Boris.


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