From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Anthony PERARD <anthony.perard@citrix.com>
Cc: "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: OVMF very slow on AMD
Date: Thu, 28 Jul 2016 11:17:09 -0400 [thread overview]
Message-ID: <4217cf61-6ac2-f568-5a6c-cc9478ffd1b1@oracle.com> (raw)
In-Reply-To: <457e48f9-9116-8c86-02c4-ac9fd9d274a1@citrix.com>
On 07/28/2016 06:54 AM, Andrew Cooper wrote:
> On 28/07/16 11:43, George Dunlap wrote:
>> On Thu, Jul 28, 2016 at 11:18 AM, Anthony PERARD
>> <anthony.perard@citrix.com> wrote:
>>> On Wed, Jul 27, 2016 at 03:45:23PM -0400, Boris Ostrovsky wrote:
>>>> On 07/27/2016 07:35 AM, Anthony PERARD wrote:
>>>>> On Wed, Jul 27, 2016 at 12:08:04PM +0100, Anthony PERARD wrote:
>>>>>> I can try to describe how OVMF is setting up the memory.
>>>>> From the start of the day:
>>>>> setup gdt
>>>>> cr0 = 0x40000023
>>>> I think this is slightly odd, with bit 30 (cache disable) set. I'd
>>>> suspect that this would affect both Intel and AMD though.
>>>>
>>>> Can you try clearing this bit?
>>> That works...
>>>
>>> I wonder why it does not appear to affect Intel or KVM.
>> Are those bits hard-coded, or are they set based on the hardware
>> that's available?
>>
>> Is it possible that the particular combination of CPUID bits presented
>> by Xen on AMD are causing a different value to be written?
>>
>> Or is it possible that the cache disable bit is being ignored (by Xen)
>> on Intel and KVM?
> If a guest has no hardware, then it has no reason to actually disable
> caches. We should have logic to catch this an avoid actually disabling
> caches when the guest asks for it.
Is this really safe to do? Can't a guest decide to disable cache to
avoid having to deal with coherency in SW?
As far as Intel vs AMD implementation in Xen, we have vmx_handle_cd()
but no corresponding SVM code. Could it be that we need to set gPAT, for
example?
-boris
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next prev parent reply other threads:[~2016-07-28 15:17 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-14 15:53 OVMF very slow on AMD Anthony PERARD
2016-07-15 13:48 ` Konrad Rzeszutek Wilk
2016-07-15 15:22 ` Boris Ostrovsky
2016-07-27 11:08 ` Anthony PERARD
2016-07-27 11:35 ` Anthony PERARD
2016-07-27 19:45 ` Boris Ostrovsky
2016-07-28 10:18 ` Anthony PERARD
2016-07-28 10:43 ` George Dunlap
2016-07-28 10:54 ` Andrew Cooper
2016-07-28 11:28 ` Anthony PERARD
2016-07-28 15:17 ` Boris Ostrovsky [this message]
2016-07-28 15:51 ` Andrew Cooper
2016-07-28 19:25 ` Boris Ostrovsky
2016-07-28 19:44 ` Andrew Cooper
2016-07-28 19:54 ` Boris Ostrovsky
2016-07-29 15:54 ` Anthony PERARD
2016-07-18 14:10 ` Anthony PERARD
2016-07-18 15:09 ` Anthony PERARD
2016-07-22 10:40 ` Dario Faggioli
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