On Mon, Dec 04, 2017 at 03:07:44PM +0100, Thomas Gleixner wrote:
> From: Andy Lutomirski <[email protected]>
>
> This allows the cpu entry area PMDs to be shared between the kernel and
> user space page tables.
>
> [ tglx: Fixed bottom of by one and added guards so other fixmaps can be
> added later ]
>
> Signed-off-by: Andy Lutomirski <[email protected]>
> Signed-off-by: Thomas Gleixner <[email protected]>
>
> ---
> arch/x86/include/asm/fixmap.h | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> --- a/arch/x86/include/asm/fixmap.h
> +++ b/arch/x86/include/asm/fixmap.h
> @@ -134,16 +134,22 @@ enum fixed_addresses {
> #ifdef CONFIG_PARAVIRT
> FIX_PARAVIRT_BOOTMAP,
> #endif
> - FIX_TEXT_POKE1, /* reserve 2 pages for text_poke() */
> - FIX_TEXT_POKE0, /* first page is last, because allocation is backward */
> #ifdef CONFIG_X86_INTEL_MID
> FIX_LNW_VRTC,
> #endif
> - /* Fixmap entries to remap the GDTs, one per processor. */
> + FIX_TEXT_POKE1, /* reserve 2 pages for text_poke() */
> + FIX_TEXT_POKE0, /* first page is last, because allocation is backward */
> +
> + /*
> + * Fixmap entries to remap the IDT, and the per cpu entry areas.
> + * Aligend to a PMD boundary.
"Aligned"
> + */
> + FIX_USR_SHARED_TOP = round_up(FIX_TEXT_POKE0 + 1, PTRS_PER_PMD),
> FIX_CPU_ENTRY_AREA_TOP,
> FIX_CPU_ENTRY_AREA_BOTTOM = FIX_CPU_ENTRY_AREA_TOP +
> (CPU_ENTRY_AREA_PAGES * NR_CPUS) - 1,
> + FIX_USR_SHARED_BOTTOM = round_up(FIX_CPU_ENTRY_AREA_BOTTOM + 2,
> PTRS_PER_PMD) - 1,
So those look like this here:
FIX_TEXT_POKE0: 0x285, va: 0xffffffffff57a000
FIX_USR_SHARED_TOP: 0x400, va: 0xffffffffff3ff000
FIX_CPU_ENTRY_AREA_TOP: 0x401, va: 0xffffffffff3fe000
FIX_CPU_ENTRY_AREA_BOTTOM: 0x458, va: 0xffffffffff3a7000
FIX_USR_SHARED_BOTTOM: 0x5ff, va: 0xffffffffff200000
and FIX_CPU_ENTRY_AREA_TOP is the one PTE before the last 4K. But we
could just as well use the last one too, no? I.e.,
FIX_USR_SHARED_TOP = round_up(FIX_TEXT_POKE0 + 1, PTRS_PER_PMD),
FIX_CPU_ENTRY_AREA_TOP = FIX_USR_SHARED_TOP,
?
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
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