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From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: hans.rosenfeld@amd.com, torvalds@linux-foundation.org,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	Arjan van de Ven <arjan@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: bisected boot regression post 2.6.25-rc3.. please revert
Date: Mon, 03 Mar 2008 14:56:17 -0800	[thread overview]
Message-ID: <47CC8211.7090704@goop.org> (raw)
In-Reply-To: <a9af8424f96a9118c6b097d9b2df79b2@kernel.crashing.org>

Segher Boessenkool wrote:
>>> so (on 32-bit) ~_PAGE_PSE is ~0x80L is 0xffffff7f, which when cast to
>>> 64-bit is 0x00000000ffffff7f,
>>
>> Actually, it is signed, so this isn't true.  Comments about unsafeness
>> still apply.
>
> It turns out that PAGE_SIZE is unsigned.  So this gives us for
>
>     (~PAGE_MASK & ~_PAGE_USER & ~_PAGE_PSE & ~_PAGE_NX)
>
> the types UL, L, L, ULL resp.
>
> The associativity of & is left-to-right, so this in turn becomes
>
>     UL, L, ULL
>
>     UL, ULL
>
>     ULL
>
> and that cast from UL to ULL doesn't sign-extend. 

I went through and made a bunch of these flags signed so that they would 
sign-extend properly in 32 vs 64 bit.  We could make them 
unconditionally 64-bit, but I'm worried that will have unforeseen 
consequences too.

In this case, PAGE_MASK should probably be signed too, so the sign 
extension happens properly.

Alternatively, they could be cast to pteval_t and/or phys_addr_t so that 
they will have an inherent size which matches the pagetable format 
(using _AT() rather than _AC()).

    J

  parent reply	other threads:[~2008-03-03 23:01 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-01 18:56 Arjan van de Ven
2008-03-03  7:46 ` Ingo Molnar
2008-03-03  9:13   ` Ingo Molnar
2008-03-03 16:41     ` Arjan van de Ven
2008-03-03 17:40       ` Ingo Molnar
2008-03-03 17:51         ` Nish Aravamudan
2008-03-03 17:55           ` Ingo Molnar
2008-03-03 17:58             ` H. Peter Anvin
2008-03-03 18:36         ` Arjan van de Ven
2008-03-03 18:44           ` Linus Torvalds
2008-03-03 22:00             ` Arjan van de Ven
2008-03-04  1:05               ` Arjan van de Ven
2008-03-04  6:53                 ` Ingo Molnar
2008-03-05 15:35                   ` Arjan van de Ven
2008-03-09 11:56             ` Ingo Molnar
2008-03-09 17:27               ` Linus Torvalds
2008-03-09 18:57                 ` Ingo Molnar
2008-03-10  2:45                 ` Jeremy Fitzhardinge
2008-03-10  4:35                 ` Paul Mackerras
2008-03-03 21:13           ` Segher Boessenkool
2008-03-03 21:22             ` Segher Boessenkool
2008-03-03 22:33               ` Segher Boessenkool
2008-03-03 22:55                 ` H. Peter Anvin
2008-03-03 22:56                 ` Jeremy Fitzhardinge [this message]
2008-03-03 23:04                   ` H. Peter Anvin
2008-03-04  6:58             ` Ingo Molnar
2008-03-03 17:15 ` Nish Aravamudan

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