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From: "Jan Beulich" <JBeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Tim Deegan <tim@xen.org>, Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v2 5/9] x86/pagewalk: Helpers for reserved bit handling
Date: Fri, 24 Mar 2017 02:25:02 -0600	[thread overview]
Message-ID: <58D4E5EE020000780014719A@prv-mh.provo.novell.com> (raw)
In-Reply-To: <eda54533-b47a-b570-c543-b64d84f4bcf0@suse.com>

>>> On 24.03.17 at 08:58, <jgross@suse.com> wrote:
> On 24/03/17 08:51, Jan Beulich wrote:
>>>>> On 24.03.17 at 06:45, <jgross@suse.com> wrote:
>>> On 23/03/17 18:35, Andrew Cooper wrote:
>>>> Would you prefer ~((uint64_t)_PAGE_PSE_PAT | (_PAGE_PSE_PAT - 1)) or
>>>> ~(_PAGE_PSE_PAT | (_PAGE_PSE_PAT - 1) | 0ULL)
>>>
>>> Wouldn't it be better to just define the _PAGE_PSE bits accordingly?
>> 
>> I don't think that's a good idea, since the flags accessors deal with
>> unsigned int quantities (see {get,put}_pte_flags()), and there's no
>> need to promote these to 64 bit operations. Otherwise you'd also
>> have to e.g. ask for _PAGE_NX_BIT to be made 1ULL << 63 instead
>> of its current 1ULL << 23.
> 
> Well, I came to my conclusion looking at the usage of _PAGE_PSE_PAT
> in do_recalc() (source file arch/x86/mm/p2m-pt.c). While being fine
> right now it will be a problem as soon as we support >16 TB hosts.
> And finding these kind of problems might be hard.

We do support such hosts (CONFIG_BIGMEM), so we should fix such
issues. Luckily a quick grep shows this to be the only problem of that
kind. The problem really only occurs when the flags accessors are
being bypassed (which sadly in a few cases is almost unavoidable).

I guess you'll submit a patch, else let me know if I should do so.

Jan


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  reply	other threads:[~2017-03-24  8:25 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-16 16:31 [PATCH v2 0/9] Fixes to pagetable handling Andrew Cooper
2017-03-16 16:31 ` [PATCH v2 1/9] x86/cpuid: Sort cpu_has_* predicates by feature number Andrew Cooper
2017-03-17 16:08   ` Jan Beulich
2017-03-16 16:31 ` [PATCH v2 2/9] x86/pagewalk: Use pointer syntax for pfec parameter Andrew Cooper
2017-03-17 16:09   ` Jan Beulich
2017-03-20 11:29   ` George Dunlap
2017-03-23 16:28   ` Tim Deegan
2017-03-16 16:31 ` [PATCH v2 3/9] x86/shadow: Drop VALID_GFN() Andrew Cooper
2017-03-23 16:30   ` Tim Deegan
2017-03-16 16:31 ` [PATCH v2 4/9] x86/pagewalk: Clean up guest_supports_* predicates Andrew Cooper
2017-03-20  8:45   ` Jan Beulich
2017-03-20 13:36     ` Andrew Cooper
2017-03-20 13:59       ` Jan Beulich
2017-03-23 17:32         ` Andrew Cooper
2017-03-24  7:19           ` Jan Beulich
2017-03-23 16:34   ` Tim Deegan
2017-03-16 16:31 ` [PATCH v2 5/9] x86/pagewalk: Helpers for reserved bit handling Andrew Cooper
2017-03-20  8:48   ` Jan Beulich
2017-03-23 16:55   ` Tim Deegan
2017-03-23 17:02     ` Andrew Cooper
2017-03-23 17:12       ` Tim Deegan
2017-03-23 17:35         ` Andrew Cooper
2017-03-24  5:45           ` Juergen Gross
2017-03-24  7:51             ` Jan Beulich
     [not found]             ` <58D4DDFF0200007800147138@suse.com>
2017-03-24  7:58               ` Juergen Gross
2017-03-24  8:25                 ` Jan Beulich [this message]
2017-03-24  9:06             ` Andrew Cooper
2017-03-24  7:47           ` Jan Beulich
2017-03-24  8:36             ` Andrew Cooper
2017-03-16 16:31 ` [PATCH v2 6/9] x86/pagewalk: Re-implement the pagetable walker Andrew Cooper
2017-03-16 16:31 ` [PATCH v2 7/9] x86/shadow: Use the pagewalk reserved bits helpers Andrew Cooper
2017-03-16 17:25   ` Andrew Cooper
2017-03-20  8:53   ` Jan Beulich
2017-03-23 16:57   ` Tim Deegan
2017-03-16 16:31 ` [PATCH v2 8/9] x86/pagewalk: Improve the logic behind setting access and dirty bits Andrew Cooper
2017-03-20  9:03   ` Jan Beulich
2017-03-23 17:09   ` Tim Deegan
2017-03-23 17:40     ` Andrew Cooper
2017-03-16 16:31 ` [PATCH v2 9/9] x86/pagewalk: non-functional cleanup Andrew Cooper
2017-03-20  9:04   ` Jan Beulich
2017-03-23 17:10   ` Tim Deegan

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