Re: [Xen-devel] [xen-unstable test] 16788: regressions - FAIL

[Tim Deegan <tim@xxxxxxx>]

At 12:06 +0000 on 04 Mar (1362398796), Jan Beulich wrote:
> >>> On 04.03.13 at 12:45, Tim Deegan <tim@xxxxxxx> wrote:
> > At 11:29 +0000 on 04 Mar (1362396574), Jan Beulich wrote:
> >> >>> On 04.03.13 at 12:12, Tim Deegan <tim@xxxxxxx> wrote:
> >> > At 10:57 +0000 on 04 Mar (1362394626), Jan Beulich wrote:
> >> >> Question - is there really no better way than this to deal with
> >> >> cross page emulated writes?
> >> > 
> >> > There probably is -- all that's wanted here is two mappings that are
> >> > guaranteed to be contiguous in virtual address.  The LDT slots were
> >> > available; it would have been better to document this use where
> >> > LDT_VIRT_START is defined, though.
> >> > 
> >> > AFAICT, we'll need to:
> >> >  - cause some equivalent pair of PTEs to be available (either per-cpu or
> >> >    per-vcpu); or
> >> >  - add a map_two_domain_pages() function to use the mapcache for this; or
> >> 
> >> Would vmap() do? Or do we expect this code path to be performance
> >> sensitive?
> > 
> > I can't really tell what vmap() is for, since it seems to have no
> > documentation, and the checkin description just says "implement vmap()".
> > But it looks plausible, and emulating page-crossing writes oughtn't to
> > be performance-sensitive.
> 
> Like this then (compile tested only so far):

> @@ -4748,14 +4743,8 @@ static void emulate_unmap_dest(struct vc
>  
>      if ( unlikely(mfn_valid(sh_ctxt->mfn2)) )
>      {
> -        unsigned long offset;
>          paging_mark_dirty(v->domain, mfn_x(sh_ctxt->mfn2));
> -        /* Undo the hacky two-frame contiguous map. */
> -        ASSERT(((unsigned long) addr & PAGE_MASK) == LDT_VIRT_START(v));
> -        offset = l1_linear_offset((unsigned long) addr);
> -        l1e_write(&__linear_l1_table[offset], l1e_empty());
> -        l1e_write(&__linear_l1_table[offset + 1], l1e_empty());
> -        flush_tlb_all();
> +        vunmap(addr - ((unsigned long)addr & ~PAGE_MASK));

I'd prefer 'vunmap((void *)((unsigned long) addr & PAGE_MASK));'.
Otherwise, Acked-by: Tim Deegan <tim@xxxxxxx>

Cheers,

Tim.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel