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

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Date:	Wed, 07 Jan 2015 05:58:26 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Alok Kataria <akataria@...are.com>
CC:	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Dunn <ddunn@...are.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"jongman.heo@...sung.com" <jongman.heo@...sung.com>
Subject: Re: [PATCH] x86: don't rely on VMWare emulating PAT MSR correctly

x86 maintainers, could you please consider taking my patch?

There have been several reports now regarding this issue, all could be
fixed using my patch.

Juergen

On 12/17/2014 05:57 AM, Alok Kataria wrote:
> Hi,
>
> On Tue, 2014-12-16 at 10:58 +0100, 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.
>
> Thanks for taking care of this, we are fine with this workaround. On
> newer version of our product, where PAT is virtualized correctly on our
> platform we will go back to using PAT, I will give it a spin sometime
> later to verify it.
>
> Acked-by: Alok N Kataria <akataria@...are.com>
>
>> Reported-by: Jongman Heo <jongman.heo@...sung.com>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> Tested-by: Jongman Heo <jongman.heo@...sung.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);
>>
>
> Alok
> N�����r��y���b�X��ǧv�^�)޺{.n�+����{����zX��.��ܨ}���Ơz�&j:+v���.����zZ+��+zf���h���~����i���z�.�w���?����&�)ߢ.f��^jǫy�m��@A�a���.0��h�.�i
>

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