Re: [Xen-devel] [PATCH] x86/HVM: drop bogus #PF raising from linear->phys translation

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 07/09/17 09:14, Jan Beulich wrote:
> Translations spanning a page boundary not resulting in physically
> contiguous addresses is not a reason to raise #PF. In fact by not doing
> so accesses of this kind are being emulated correctly thanks to the
> fallback logic in the insn emulator's REP MOVS/STOS/INS/OUTS handling
> (non-string accesses to such locations are being split elsewhere and
> hence have been working fine already).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -566,15 +566,12 @@ static int hvmemul_linear_to_phys(
>              if ( pfec & (PFEC_page_paged | PFEC_page_shared) )
>                  return X86EMUL_RETRY;
>              done /= bytes_per_rep;
> -            *reps = done;
>              if ( done == 0 )
>              {
>                  ASSERT(!reverse);
> -                if ( npfn != gfn_x(INVALID_GFN) )
> -                    return X86EMUL_UNHANDLEABLE;
> -                x86_emul_pagefault(pfec, addr & PAGE_MASK, 
> &hvmemul_ctxt->ctxt);
> -                return X86EMUL_EXCEPTION;
> +                return X86EMUL_UNHANDLEABLE;

I dont follow your reasoning.  The pagefault path is only reachable when
npfn is INVALID_GFN, which means a pagewalk did fail.

It might be cleaner to split out the pagefault path out into a block at
the bottom, but I think the logic is correct as-is.

~Andrew

>              }
> +            *reps = done;
>              break;
>          }
>  
>
>
>


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