From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
"Ian Jackson" <iwj@xenproject.org>,
Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH] x86/kexec: Fix crash on transition to a 32bit kernel on AMD hardware
Date: Tue, 2 Nov 2021 13:54:18 +0100 [thread overview]
Message-ID: <225c0ac3-cc57-d26b-acd1-b62dbcffd002@suse.com> (raw)
In-Reply-To: <20211028232658.20637-1-andrew.cooper3@citrix.com>
On 29.10.2021 01:26, Andrew Cooper wrote:
> The `ljmp *mem` instruction is (famously?) not binary compatible between Intel
> and AMD CPUS. The AMD-compatible version would require .long to be .quad in
> the second hunk.
From all sources I have the incompatibility is only with REX.W: Intel
honors it (allowing a mem64:16) operand, while AMD ignores it (using
the same mem32:16 operand form as without REX.W). All the same as for
L{F,G,S}S. Hence I do not see why the present form of (32-bit) LJMP
would be a problem anywhere.
> Switch to using lretq, which is compatible between Intel and AMD, as well as
> being less logic overall.
I certainly don't mind the switch to LRETQ, but then the reasoning
will imo need to change.
Jan
prev parent reply other threads:[~2021-11-02 12:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-28 23:26 [PATCH] x86/kexec: Fix crash on transition to a 32bit kernel on AMD hardware Andrew Cooper
2021-11-01 10:53 ` Ian Jackson
2021-11-01 11:10 ` Andrew Cooper
2021-11-01 12:13 ` Ian Jackson
2021-11-01 17:32 ` Andrew Cooper
2021-11-02 15:54 ` Ian Jackson
2021-11-02 12:54 ` Jan Beulich [this message]
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