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Wed, 21 Oct 2020 21:16:13 +0800 Received: from zxbjmbx1.zhaoxin.com ([fe80::290a:f538:51e7:1416]) by zxbjmbx1.zhaoxin.com ([fe80::290a:f538:51e7:1416%16]) with mapi id 15.01.1979.003; Wed, 21 Oct 2020 21:16:13 +0800 From: FelixCui-oc To: Paolo Bonzini , Alex Williamson Subject: =?gb2312?B?tPC4tDogW1BBVENIIDEvMV0gU2tpcCBmbGF0dmlld19zaW1wbGlmeSgpIGZv?= =?gb2312?Q?r_cpu_vendor_zhaoxin?= Thread-Topic: [PATCH 1/1] Skip flatview_simplify() for cpu vendor zhaoxin Thread-Index: AQHWo6+lIFwCGFufXkSJFIAohPLGXamZlV6AgAUx0wCAAPEVAIAA32uAgACU/oCAAN+P8Q== Date: Wed, 21 Oct 2020 13:16:13 +0000 Message-ID: <6b7179fb801c4ef1919153ebee85c256@zhaoxin.com> References: <20201016112933.14856-1-FelixCui-oc@zhaoxin.com> <20201016112933.14856-2-FelixCui-oc@zhaoxin.com> <20201019130206.1d3baffc@w520.home> <4d2b96cb-8f7f-2598-39e6-4cf0f61d567b@redhat.com> <20201020164437.5e3cb4ce@w520.home>, <783b5ef0-277c-363d-f342-7c0351f9ac16@redhat.com> In-Reply-To: <783b5ef0-277c-363d-f342-7c0351f9ac16@redhat.com> Accept-Language: zh-CN, en-US Content-Language: zh-CN X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.29.8.40] Content-Type: multipart/alternative; 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charset="gb2312" Content-Transfer-Encoding: quoted-printable

hi Paolo,

>Felix, did you = identify the regions whose simplification causes the bug?
>Is this RAM (for e= xample due to the PAM registers) or something else?


yes, this bug is ca= used by write PAM register.The actual situation is that the

properties of some = ranges are changed from RW to readonly.This situation 

will cause the old = ranges to be unmapped.


Best regards=

Felixcui-oc<= /p>


=B7=A2=BC=FE=C8=CB: Paolo= Bonzini <pbonzini@redhat.com>
=B7=A2=CB=CD=CA=B1=BC=E4: 2020=C4=EA10=D4=C221=C8=D5 15:37:53
=CA=D5=BC=FE=C8=CB: Alex Williamson
=B3=AD=CB=CD: FelixCui-oc; Richard Henderson; Eduardo Habkost; qemu-= devel@nongnu.org; RockCui-oc; Tony W Wang-oc; CobeChen-oc
=D6=F7=CC=E2: Re: [PATCH 1/1] Skip flatview_simplify() for cpu vendo= r zhaoxin
 
On 21/10/20 00:44, Alex Williamson wrote:
> Do we necessarily need a memory map ioctl for this or could it be the<= br> > QEMU code that compares the old and new maps to trigger map and unmap<= br> > ioctls?  For example (aiui) our race is that if we have contiguou= s
> memory regions A and B and flatview_simplify() tries to expand A and > delete B we'll see a series of listener notifications deleting A and B=
> and adding A'.  But the vfio QEMU code could parse the memory map= to
> determine that old A + B is functionally equivalent to A' and do > nothing.

I think the issue is a bit different, and in fact there are two sides of the same issue.  Say you have A (large) and it is replaced by A'
(smaller) + B, then:

* the first part of A disappears for a moment before A' appears.  This=
is something that QEMU can work around, by not doing anything

* the second part of A disappears for a moment before B appears.  This=
is the root API issue and not something that QEMU can work around; and
in fact it is not even fixed by removing flatview_simplify.

Felix, did you identify the regions whose simplification causes the bug?  Is this RAM (for example due to the PAM registers) or something else?=

Paolo

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