From: "Barry Silverman" <barry@disus.com>
To: "Ronald G. Minnich" <rminnich@lanl.gov>,
Himanshu Raj <rhim@cc.gatech.edu>
Cc: xen-devel@lists.sourceforge.net
Subject: RE: xen and tls (fwd)
Date: Mon, 14 Feb 2005 12:07:36 -0500 [thread overview]
Message-ID: <IGEMLBGAECDFPIKMIMLCOEOICGAA.barry@disus.com> (raw)
In-Reply-To: <Pine.LNX.4.58.0502140952400.10141@enigma.lanl.gov>
As I recall, tls maps negative offsets >0xFF000000 (from segment registers
FS, GS) into the kernel address space (IE >0xa8000000), and this conflicts
with xen's virtual address mapping.
Xen lives mapped into high virtual memory but inaccessible to the guest
kernels - however the whole guest kernel address space is accessible to xen.
Keir Fraser developed an instruction emulator/code patcher in the page fault
code that detected these large offsets from FS/GS, and then fixed them up...
I recall that the emulator ended up getting called way for often than anyone
wanted and ran slowly. The "not-to-use" TLS recommendation followed from
that.
Barry Silverman
-----Original Message-----
From: xen-devel-admin@lists.sourceforge.net
[mailto:xen-devel-admin@lists.sourceforge.net]On Behalf Of Ronald G.
Minnich
Sent: Monday, February 14, 2005 11:53 AM
To: Himanshu Raj
Cc: xen-devel@lists.sourceforge.net
Subject: Re: [Xen-devel] xen and tls (fwd)
On Mon, 14 Feb 2005, Himanshu Raj wrote:
> I believe it is due to the use of both +ve and -ve offsets by TLS. It
becomes
> a nightmare to manage it with segmentation, and system has to emulate -ve
> offsets by converting to +ve ones etc. I am still learning more on this.
I vaguely remember this discussion, I just wish I could remember more.
ron
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next prev parent reply other threads:[~2005-02-14 17:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-02-14 15:53 xen and tls (fwd) Ronald G. Minnich
2005-02-14 16:05 ` Anthony Liguori
2005-02-14 16:33 ` Himanshu Raj
2005-02-14 16:52 ` Ronald G. Minnich
2005-02-14 17:07 ` Barry Silverman [this message]
2005-02-14 17:02 ` Michael A Fetterman
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