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From: Jan Beulich <jbeulich@suse.com>
To: paul@xen.org
Cc: sstabellini@kernel.org, julien@xen.org, wl@xen.org,
	konrad.wilk@oracle.com, george.dunlap@eu.citrix.com,
	andrew.cooper3@citrix.com, ian.jackson@eu.citrix.com,
	george.dunlap@citrix.com, jeff.kubascik@dornerworks.com, "'Xia,
	Hongyan'" <hongyxia@amazon.com>,
	stewart.hildebrand@dornerworks.com,
	xen-devel@lists.xenproject.org,
	'David Woodhouse' <dwmw2@infradead.org>
Subject: Re: [Xen-devel] [PATCH 2/2] xen/mm: Introduce PG_state_uninitialised
Date: Wed, 18 Mar 2020 12:12:04 +0100	[thread overview]
Message-ID: <68f41288-31dc-bb16-fd09-5a818cd8f3e9@suse.com> (raw)
In-Reply-To: <006401d5fd11$cdf31930$69d94b90$@xen.org>

On 18.03.2020 11:41, Paul Durrant wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: 18 March 2020 10:10
>> To: paul@xen.org
>> Cc: 'David Woodhouse' <dwmw2@infradead.org>; sstabellini@kernel.org; julien@xen.org; wl@xen.org;
>> konrad.wilk@oracle.com; george.dunlap@eu.citrix.com; andrew.cooper3@citrix.com;
>> ian.jackson@eu.citrix.com; george.dunlap@citrix.com; jeff.kubascik@dornerworks.com; 'Xia, Hongyan'
>> <hongyxia@amazon.com>; stewart.hildebrand@dornerworks.com; xen-devel@lists.xenproject.org
>> Subject: Re: [PATCH 2/2] xen/mm: Introduce PG_state_uninitialised
>>
>> On 18.03.2020 09:53, Paul Durrant wrote:
>>>> -----Original Message-----
>>>> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf Of David Woodhouse
>>>> Sent: 17 March 2020 22:15
>>>>
>>>> On Thu, 2020-02-20 at 12:59 +0100, Jan Beulich wrote:
>>>>> On 07.02.2020 19:04, David Woodhouse wrote:
>>>>>> --- a/xen/arch/x86/mm.c
>>>>>> +++ b/xen/arch/x86/mm.c
>>>>>> @@ -488,7 +488,8 @@ void share_xen_page_with_guest(struct page_info *page, struct domain *d,
>>>>>>
>>>>>>        page_set_owner(page, d);
>>>>>>        smp_wmb(); /* install valid domain ptr before updating refcnt. */
>>>>>> -    ASSERT((page->count_info & ~PGC_xen_heap) == 0);
>>>>>> +    ASSERT((page->count_info & ~PGC_xen_heap) == PGC_state_inuse ||
>>>>>> +           (page->count_info & ~PGC_xen_heap) == PGC_state_uninitialised);
>>>>>
>>>>> Can uninitialized pages really make it here?
>>>>
>>>> Yep, we share the low 1MiB with dom_io.
>>>>
>>>
>>> OOI anyone know why we do this? Is it actually necessary?
>>
>> Yes, for Dom0 to be able to access things like EBDA, IBFT, or data
>> found in BIOS space.
>>
> 
> Ok. I am still wondering why dom0's low 1MiB of pfn space is not
> simply mapped 1:1 though. Just historical?

Well, in a way perhaps. Using the DomIO approach is less of a special
case than mapping some arbitrary range 1:1. Furthermore Dom0 being PV
wouldn't necessarily expect any BIOS in its PFN range there, but
rather views it as normal RAM.

Jan

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  reply	other threads:[~2020-03-18 11:12 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-04 15:14 [Xen-devel] [XEN PATCH v2 1/2] Check zone before merging adjacent blocks in heap Stewart Hildebrand
2020-02-04 15:14 ` [Xen-devel] [DO NOT APPLY XEN PATCH v2 2/2] Test case for buddy allocator merging issue Stewart Hildebrand
2020-02-04 15:22 ` [Xen-devel] [XEN PATCH v2 1/2] Check zone before merging adjacent blocks in heap Jan Beulich
2020-02-04 15:37   ` George Dunlap
2020-02-05  9:50     ` David Woodhouse
2020-02-05 10:02       ` Jan Beulich
2020-02-05 10:24         ` David Woodhouse
2020-02-05 10:49           ` Jan Beulich
2020-02-05 11:23             ` David Woodhouse
2020-02-05 13:37               ` Jan Beulich
2020-02-05 14:12                 ` David Woodhouse
2020-02-07 15:49                   ` David Woodhouse
2020-02-07 15:57                     ` [Xen-devel] [PATCH 1/2] xen/mm: fold PGC_broken into PGC_state bits David Woodhouse
2020-02-07 20:27                       ` Julien Grall
2020-02-09 13:22                         ` David Woodhouse
2020-02-09 17:59                           ` Julien Grall
2020-03-17 21:39                         ` David Woodhouse
2020-02-20 11:10                       ` Jan Beulich
2020-03-17 21:52                         ` David Woodhouse
2020-03-18  9:56                           ` Jan Beulich
2020-03-18 12:31                             ` Julien Grall
2020-03-18 13:23                               ` Jan Beulich
2020-03-18 17:13                               ` David Woodhouse
2020-03-19  8:49                                 ` Jan Beulich
2020-03-19 10:26                                   ` David Woodhouse
2020-03-19 11:59                                     ` Jan Beulich
2020-03-19 13:54                                       ` David Woodhouse
2020-03-19 14:46                                         ` Jan Beulich
2020-02-07 15:57                     ` [Xen-devel] [PATCH 2/2] xen/mm: Introduce PG_state_uninitialised David Woodhouse
2020-02-07 16:30                       ` Xia, Hongyan
2020-02-07 16:32                         ` David Woodhouse
2020-02-07 16:40                           ` Xia, Hongyan
2020-02-07 17:06                             ` David Woodhouse
2020-02-07 18:04                               ` David Woodhouse
2020-02-20 11:59                                 ` Jan Beulich
2020-02-20 13:27                                   ` Julien Grall
2020-03-17 22:15                                   ` David Woodhouse
2020-03-18  8:53                                     ` Paul Durrant
2020-03-18 10:10                                       ` Jan Beulich
2020-03-18 10:41                                         ` Paul Durrant
2020-03-18 11:12                                           ` Jan Beulich [this message]
2020-03-18 10:03                                     ` Jan Beulich
2020-03-18 12:11                                       ` David Woodhouse
2020-03-18 13:27                                         ` Jan Beulich
2020-02-05 10:22       ` [Xen-devel] [XEN PATCH v2 1/2] Check zone before merging adjacent blocks in heap Julien Grall
2020-02-05 10:32         ` David Woodhouse
2020-02-05 11:36         ` David Woodhouse
2020-02-04 15:37   ` Stewart Hildebrand

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