Re: [Xen-devel] [PATCH] xen/SandyBridge: reserve pages when integrated graphics

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, March 22, 2013 6:27 PM
> To: Hao, Xudong
> Cc: xen-devel@xxxxxxxxxxxxx; keir@xxxxxxx
> Subject: Re: [PATCH] xen/SandyBridge: reserve pages when integrated graphics
> 
> >>> On 22.03.13 at 08:48, Xudong Hao <xudong.hao@xxxxxxxxx> wrote:
> > +char *__init get_platform_badpages(void)
> > +{
> > +    u32 igd_id;
> > +    static char __initdata bad_pfns[] =
> > +                {"0x20050,0x20110,0x20130,0x20138,0x40004"};
> 
> With quite a bit of trouble I managed to find all applicable spec
> updates, but none of them mentions 0x20110.
> 
I did not get detail spec either, but linux kernel has remove this page 
0x20110000 already for the same reason, refer to commit: 
a9acc5365dbda29f7be2884efb63771dc24bd815

> > +#ifdef CONFIG_X86
> > +    /*
> > +     * Here we put platform-specific memory range workarounds, i.e.
> > +     * memory known to be corrupt or otherwise in need to be reserved on
> > +     * specific platforms.
> > +     * We get these certain pages and put them in bad-page list.
> > +     */
> > +    p = get_platform_badpages();
> > +    if ( p )
> > +        remove_bad_pages(p);
> > +#endif
> 
> I also dislike the re-use of the command line parsing code here.
> There's no need to do this for a list of known MFNs, the hook
> could provide an array of unsigned long instead.
> 
Right. bootmem_region_zap() can do this directly.

> And finally it is my understanding that these pages aren't bad in
> any way, it must only be ensured they don't get passed to the
> graphics engine. Which in particular means using these pages for
> Xen's own purposes (i.e. not passing them to any domain) would
> be quite fine. Yes, I realize it's only a handful of pages, but it
> seems odd anyway.
> 
We all know these pages can be used for Xen, but not for domains. But as you 
said, it's only 5 pages, the simplest solution is removing them in xen 
starting, so that they don't be allocate to any domains.

-Thanks
Xudong


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