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Re: [Xen-devel] [PATCH] add support for XCHG instruction accessing APIC

To: Boris Ostrovsky <bostrovsky@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] add support for XCHG instruction accessing APIC
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 5 Apr 2006 10:50:54 +0100
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On 4 Apr 2006, at 22:24, Boris Ostrovsky wrote:

32-bit SMP Linux uses xchg instruction to access APIC (see
apic_write_atomic()). Attached is patch that adds support for
this instruction.

The patch also fixes missed dependencies (in xen/Rules.mk) on
header files in include/asm-x86/hvm.

I wonder if it is worth adding the locking? xchg is only used to write to broken APICs -- the OS does not care about the returned value. The APIC is implemented entirely in Xen, so the lock isn't held across an ioreq round-trip to qemu-dm, right?

 -- Keir

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