linux-kernel - Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR

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Message-ID: <55A2B8F7.1050805@linux.intel.com>
Date:	Mon, 13 Jul 2015 02:59:03 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	pbonzini@...hat.com, gleb@...nel.org, mtosatti@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR



On 07/13/2015 01:33 AM, Alex Williamson wrote:
> On Wed, 2015-05-13 at 14:42 +0800, Xiao Guangrong wrote:
>> There are some bugs in current get_mtrr_type();
>> 1: bit 1 of mtrr_state->enabled is corresponding bit 11 of
>>     IA32_MTRR_DEF_TYPE MSR which completely control MTRR's enablement
>>     that means other bits are ignored if it is cleared
>>
>> 2: the fixed MTRR ranges are controlled by bit 0 of
>>     mtrr_state->enabled (bit 10 of IA32_MTRR_DEF_TYPE)
>>
>> 3: if MTRR is disabled, UC is applied to all of physical memory rather
>>     than mtrr_state->def_type
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
>> ---
>>   arch/x86/kvm/mmu.c | 14 ++++++--------
>>   1 file changed, 6 insertions(+), 8 deletions(-)
>
>
> I'm seeing a significant regression in boot performance on Intel
> hardware with assigned devices that bisects back to this patch.  There's
> a long delay with Seabios between the version splash and execution of
> option ROMs, and a _very_ long delay with OVMF before the display is
> initialized.  The delay is long enough that users are reporting their
> previously working VM is hung with 100% CPU usage on v4.2-rc1.  Thanks,
>

Alex, thanks for your report. I will try to reproduce and fix it asap.
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