Re: [PATCH for-4.6] libxl: move calling libxl__arch_domain_construct_memmap to right place

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 8/5/2015 7:25 PM, Wei Liu wrote:
> On Wed, Aug 05, 2015 at 12:06:22PM +0100, Ian Campbell wrote:
>> On Wed, 2015-08-05 at 11:58 +0100, Wei Liu wrote:
>> > On Wed, Aug 05, 2015 at 11:48:55AM +0100, Ian Campbell wrote:
>> > > On Wed, 2015-08-05 at 11:43 +0100, Wei Liu wrote:
>> > > > On Wed, Aug 05, 2015 at 11:38:54AM +0100, Ian Campbell wrote:
>> > > > > On Wed, 2015-08-05 at 11:23 +0100, Wei Liu wrote:
>> > > > > > This function was called in the wrong place, because both
>> > > > > > libxl__vnuma_build_vmemrange_hvm and xc_hvm_build rely on its
>> > > > > > output.
>> > > > >
>> > > > > What is the effect of this call being in the wrong place?
>> > > > > Presumably
>> > > > > one or
>> > > > > the other of those functions reaches the wrong conclusion?
>> > > >
>> > > > Originally, by the time that function got called, all guest pages
>> > > > were
>> > > > already populated.  The end result is E820 map disagrees with what
>> > > > vNUMA
>> > > > says and what address ranges memory actually resides, i.e. risk of
>> > > > guest
>> > > > accessing region that doesn't have backing pages.
>> > >
>> > > Ouch. This should certainly be explained in the commit message.
>> > >
>> > > With that: Acked-by: Ian Campbell <ian.campbell@citrix.com>
>> > >
>> >
>> > I will post v2 shortly with that information in commit message.
>> >
>> > > Although perhaps we should wait for confirmation this fix doesn't
>> > > regress
>> > > RMRR somehow?
>> > >
>> >
>> > I doubt it will. The code as-is is already broken for RMRR. But let's
>> > wait till tomorrow for Tiejun to reply.
>> >
>> > If he doesn't reply by tomorrow, I suggest we apply v2 first and
>> > fix up any subsequent issues later.
>>
>> Agreed.
>
> Actually I want to retract this patch. I confused hvm path with pv path
> and drew my conclusion when looking at both code paths.
>
> In hvm path, neither libxl__vnuma_build_vmemragen_hvm nor xc_hvm_build
> depends on output of libxl__arch_domain_construct_memmap (in fact it
> doesn't change anything). So the code is OK.
>
> In pv path, there is a path which relies on having a valid E820 map
> first, but that path 1) relies on host E820 map; 2) doesn't involve RMRR
> support.
>
> In the end, moving that function call has no effect whatsoever.

Sorry I don't go into this details but seems I have nothing to do about 
this, ultimately. Right?

Thanks
Tiejun

>
> Sorry for the noise!
>
> Wei.
>
>