Jeremy Fitzhardinge wrote:
> Jeremy Fitzhardinge wrote:
>
>> Hm, I don't think this interface will work for Xen. In Xen, whenever a
>> pagetable page gets mapped, it must be mapped RO. map_pt_hook gets
>> called after the mapping has already been created, so its too late for Xen.
>>
>> I was planning on adding kmap_atomic_pte() for use in pte_offset_map*(),
>> which would be wired through to paravirt_ops to allow Xen to make this a
>> RO mapping. Would this be sufficient for you to do your vmi thing?
>>
>>
>
> Something like this (compiled, untested).
>
> J
>
> diff -r 972e84c265cf arch/i386/kernel/paravirt.c
> --- a/arch/i386/kernel/paravirt.c Thu Mar 01 19:12:49 2007 -0800
> +++ b/arch/i386/kernel/paravirt.c Thu Mar 01 19:38:42 2007 -0800
> @@ -32,6 +32,7 @@
> #include <asm/fixmap.h>
> #include <asm/apic.h>
> #include <asm/tlbflush.h>
> +#include <asm/highmem.h>
>
> /* nop stub */
> void _paravirt_nop(void)
> @@ -605,6 +606,8 @@ struct paravirt_ops paravirt_ops = {
>
> .kpte_clear_flush = native_kpte_clear_flush,
>
> + .kmap_atomic_pte = native_kmap_atomic_pte,
> +
> #ifdef CONFIG_X86_PAE
> .set_pte_atomic = native_set_pte_atomic,
> .set_pte_present = native_set_pte_present,
> diff -r 972e84c265cf arch/i386/mm/highmem.c
> --- a/arch/i386/mm/highmem.c Thu Mar 01 19:12:49 2007 -0800
> +++ b/arch/i386/mm/highmem.c Thu Mar 01 19:38:42 2007 -0800
> @@ -26,7 +26,7 @@ void kunmap(struct page *page)
> * However when holding an atomic kmap is is not legal to sleep, so atomic
> * kmaps are appropriate for short, tight code paths only.
> */
> -void *kmap_atomic(struct page *page, enum km_type type)
> +void *_kmap_atomic(struct page *page, enum km_type type, pgprot_t prot)
> {
> enum fixed_addresses idx;
> unsigned long vaddr;
> @@ -41,9 +41,14 @@ void *kmap_atomic(struct page *page, enu
> return page_address(page);
>
> vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
> - set_pte(kmap_pte-idx, mk_pte(page, kmap_prot));
> + set_pte(kmap_pte-idx, mk_pte(page, prot));
>
> return (void*) vaddr;
> +}
> +
> +void *kmap_atomic(struct page *page, enum km_type type)
> +{
> + return _kmap_atomic(page, type, kmap_prot);
> }
>
Yeah, actually that does work, since you pass the km_type, we can use
that. But I would rather not respin this for 2.6.21; getting this 100%
right can be tricky, and we've already done a good deal of testing on
this patch the way it is. Do you have any objection to me creating a
patch for -mm tree that implements kmap_atomic_pte the way you have
described above and attaching it to the Xen patch series, but leaving
the current patch as is for now?
Thanks, (and thanks for the suggestion - I was a little worried about
how it would play with Xen when HIGHPTE support came around, but it
looks like it will work for both of us with just one paravirt-op).
Zach
