Re: [Xen-devel] [PATCH v3 25/25] x86/shadow: fold sh_x86_emulate_{write, cmpxchg}() into their only callers

[Tim Deegan <tim@xxxxxxx>]

Hi,

At 01:42 -0700 on 05 Feb (1517794959), Jan Beulich wrote:
> >>> On 02.02.18 at 17:52, <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 07/12/17 14:19, Jan Beulich wrote:
> >> +    case 1: prev = cmpxchg((uint8_t  *)ptr, old, new); break;
> >> +    case 2: prev = cmpxchg((uint16_t *)ptr, old, new); break;
> >> +    case 4: prev = cmpxchg((uint32_t *)ptr, old, new); break;
> >> +    case 8: prev = cmpxchg((uint64_t *)ptr, old, new); break;
> >> +    default:
> >> +        SHADOW_PRINTK("cmpxchg size %u is not supported\n", bytes);
> > 
> > Given the earlier patches in the series, is it worth introducing case 16
> > here?
> 
> In a follow-up patch this could be an option (unless Tim knows a
> reason why this might be a bad idea), but I certainly wouldn't want
> to do so here.

I agree that adding the 16 case shouldn't happen in this patch, and I
don't see a need for it.  Unless we think guest OSes will use 16-byte
atomic ops to update their 8-byte PTEs, the shadow code is probably
better off taking that as a hint to unshadow.

Cheers,

Tim.

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