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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.09.17 at 12:17, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 07/09/17 09:14, Jan Beulich wrote:
>> --- 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.

Hmm, good point. Yet the code as is definitely is not correct, as
it causes the guest to triple-fault with the hvmloader test
changes just sent. But since what you say regarding the #PF is
true, it looks like it's really just the "*reps = done" placement
which is causing the bad behavior; let me try with just that one
moved to the proper place(s).

Jan


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