On Mon, 2009-06-15 at 16:30 +0100, Hugh Dickins wrote: > On Mon, 15 Jun 2009, Peter Zijlstra wrote: > > > > The below would fix it, but that's getting rather ugly :-/, > > alternatively I would have to introduce something like > > pte_offset_map_irq() which would make the irq/nmi detection and leave > > the regular code paths alone, however that would mean either duplicating > > the gup_fast() pagewalk or passing down a pte function pointer, which > > would only duplicate the gup_pte_range() bit, neither is really > > attractive... > > > Index: linux-2.6/arch/x86/include/asm/pgtable_32.h > > =================================================================== > > --- linux-2.6.orig/arch/x86/include/asm/pgtable_32.h > > +++ linux-2.6/arch/x86/include/asm/pgtable_32.h > > @@ -49,7 +49,10 @@ extern void set_pmd_pfn(unsigned long, u > > #endif > > > > #if defined(CONFIG_HIGHPTE) > > -#define __KM_PTE (in_nmi() ? KM_NMI_PTE : KM_PTE0) > > +#define __KM_PTE \ > > + (in_nmi() ? KM_NMI_PTE : \ > > + in_irq() ? KM_IRQ_PTE : \ > > + KM_PTE0) > > #define pte_offset_map(dir, address) \ > > ((pte_t *)kmap_atomic_pte(pmd_page(*(dir)), __KM_PTE) + \ > > pte_index((address))) > > Yes, that does look ugly! > > I've not been following the background to this, We need/want to do a user-space stack walk from IRQ/NMI context. The NMI bit means we cannot simply use __copy_from_user_inatomic() since that will still fault (albeit not page), and the fault return path invokes IRET which will terminate the NMI context. Therefore I wrote a copy_from_user_nmi() variant that is based of of __get_user_pages_fast() (a variant that doesn't fall back to the regular GUP), but that means we get 2 kmap_atomic()s, one for HIGHPTE and one for the user page. So this introduces the pte map from IRQ context and one from NMI context. > but I've often > wondered if a kmap_push() and kmap_pop() could be useful, > allowing you to reuse the slot in between - any use here? Yes, that would be much nicer, although less we would loose some of the type validation that lives in -mm, (along with a massive overhaul of the current kmap_atomic usage). Hmm, if we give each explicit type an level and ensure the new push()'ed type's level <= the previous one, we'd still have the full nesting validation and such.. I'll look into doing this. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html