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[Xen-devel] Re: [PATCH 3/5] xl: implement parsing of cpuid parameter and

To: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 3/5] xl: implement parsing of cpuid parameter and translate to Xen interface
From: Andre Przywara <andre.przywara@xxxxxxx>
Date: Thu, 16 Sep 2010 20:49:08 +0200
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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Ian Campbell wrote:
On Thu, 2010-09-16 at 14:08 +0100, Andre Przywara wrote:
Parses a string enumerating cpuid flags and their behavior.
The syntax is: cpuid = "host,<flagname>=[01xks],..."
0: clear this flag
1: set this flag
x: don't care, use the default handling
k: use the host value
s: as k, but keep stable across migrations

Instead of the bits there can also be numbers passed (hex or dec),
like: family=0x10,model=4

Isn't this ambiguous?
No, since I don't support this legacy multi-bit syntax in the new format. I cannot think of a use-case for "keep the third bit in the family number". The above characters are just for single bit flags. Multi-bit flags need a number or a single character that gets multiplied ([xks]). The patch description is a bit vague in this respect, I will fix it with a documentation patch later.

Thanks for looking closely!


0x10 could be a hex number (i.e. 16 decimal) but it could be "(0) clear,
(x) don't care, (1) set, (0) clear". (i.e. either 2 or 6 depending on
the eventual value for the don't care)


Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448-3567-12

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