linux-kernel - Re: [Patch RESEND] x86: don't rely on VMWare emulating PAT MSR correctly

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Message-ID: <1421644471.941.25.camel@akataria-dtop.eng.vmware.com>
Date:	Mon, 19 Jan 2015 05:13:00 +0000
From:	Alok Kataria <akataria@...are.com>
To:	"jgross@...e.com" <jgross@...e.com>
CC:	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"jongman.heo@...sung.com" <jongman.heo@...sung.com>
Subject: Re: [Patch RESEND] x86: don't rely on VMWare emulating PAT MSR
 correctly

Juergen, thanks for following up on this. 

X86 maintainers - If it helps let me also confirm that without this
patch the latest kernels *always* crash on VMware guest running HWv10
and earlier.

Please include the fix at your earliest. 

Thanks,
Alok

On Mon, 2015-01-19 at 06:05 +0100, Juergen Gross wrote:
> PING!
> 
> The patch repairs a bug with VMWARE, which has been reported by several
> users. All of them have confirmed the patch is working. And VMWARE has
> acked the patch. What else do you need to take it? It is available for
> over a month now!
> 
> Juergen
> 
> On 01/12/2015 06:15 AM, Juergen Gross wrote:
> > VMWare seems not to emulate the PAT MSR correctly: reaeding
> > MSR_IA32_CR_PAT returns 0 even after writing another value to it.
> >
> > Detect this bug and don't use the read value if it is 0.
> >
> > Commit bd809af16e3ab1f8d55b3e2928c47c67e2a865d2 ("x86: Enable PAT to
> > use cache mode translation tables") triggers this VMWare bug when the
> > kernel is booted as a VMWare guest.
> >
> > Reported-by: Jongman Heo <jongman.heo@...sung.com>
> > Signed-off-by: Juergen Gross <jgross@...e.com>
> > Tested-by: Jongman Heo <jongman.heo@...sung.com>
> > Acked-by: Alok N Kataria <akataria@...are.com>
> > ---
> >   arch/x86/mm/pat.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> > index edf299c..7ac6869 100644
> > --- a/arch/x86/mm/pat.c
> > +++ b/arch/x86/mm/pat.c
> > @@ -234,8 +234,13 @@ void pat_init(void)
> >   	      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
> >
> >   	/* Boot CPU check */
> > -	if (!boot_pat_state)
> > +	if (!boot_pat_state) {
> >   		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> > +		if (!boot_pat_state) {
> > +			pat_disable("PAT read returns always zero, disabled.");
> > +			return;
> > +		}
> > +	}
> >
> >   	wrmsrl(MSR_IA32_CR_PAT, pat);
> >
> >
>