From: Anthony PERARD <anthony.perard@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
George Dunlap <george.dunlap@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: OVMF very slow on AMD
Date: Thu, 28 Jul 2016 12:28:11 +0100 [thread overview]
Message-ID: <20160728112811.GQ1835@perard.uk.xensource.com> (raw)
In-Reply-To: <457e48f9-9116-8c86-02c4-ac9fd9d274a1@citrix.com>
On Thu, Jul 28, 2016 at 11:54:27AM +0100, 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.
For KVM/QEMU, the OVMF binary is loaded in a 'CFI parallel flash', which
is map via mmio, so it is executed from a device memory. The memory
region is marked as rom_device.
--
Anthony PERARD
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next prev parent reply other threads:[~2016-07-28 11:28 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 [this message]
2016-07-28 15:17 ` Boris Ostrovsky
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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