From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xen.org>,
"Wei Liu" <wei.liu2@citrix.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v2 4/5] x86/pv: Drop {compat_, }create_bounce_frame() and use the C version instead
Date: Fri, 7 Sep 2018 15:17:46 +0100 [thread overview]
Message-ID: <e35d87d0-227b-c2a4-f70f-ebba1cb41796@citrix.com> (raw)
In-Reply-To: <5A9D1B9202000078001AE6B4@prv-mh.provo.novell.com>
On 05/03/18 09:27, Jan Beulich wrote:
>>>> On 27.02.18 at 15:50, <andrew.cooper3@citrix.com> wrote:
>> -compat_create_bounce_frame:
>> - ASSERT_INTERRUPTS_ENABLED
>> - mov %fs,%edi
>> - ASM_STAC
>> - testb $2,UREGS_cs+8(%rsp)
>> - jz 1f
>> - /* Push new frame at registered guest-OS stack base. */
>> - movl VCPU_kernel_sp(%rbx),%esi
>> -.Lft1: mov VCPU_kernel_ss(%rbx),%fs
> Note how we did take into consideration the segment base here;
> pv_create_bounce_frame() doesn't. Hence while the patch here
> is
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> I'm afraid I have to withdraw the respective tag for the earlier one
> (despite realizing that there are other places where we [wrongly]
> assume stack segments to be flat).
For the failsafe callback, %ss is set to be flat, and then a bounce
frame is created at the current kernel_sp.
Despite the impression the API might give, a 32bit PV kernel cannot use
a non-flat stack segment. No PV guest (not even MiniOS) uses a non-flat
layout, so while this is a change of behaviour, its not going to break
anything.
~Andrew
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next prev parent reply other threads:[~2018-09-07 14:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 14:50 [PATCH v2 0/5] x86: Lift create_exception_frame() up out of C Andrew Cooper
2018-02-27 14:50 ` [PATCH v2 1/5] x86/entry: Correct comparisons against boolean variables Andrew Cooper
2018-03-02 16:27 ` Jan Beulich
2018-03-02 17:32 ` Wei Liu
2018-02-27 14:50 ` [PATCH v2 2/5] x86/pv: Drop int80_bounce from struct pv_vcpu Andrew Cooper
2018-02-27 14:50 ` [PATCH v2 3/5] x86/pv: Introduce pv_create_exception_frame() Andrew Cooper
2018-03-02 16:44 ` Jan Beulich
2018-02-27 14:50 ` [PATCH v2 4/5] x86/pv: Drop {compat_, }create_bounce_frame() and use the C version instead Andrew Cooper
2018-03-05 9:27 ` Jan Beulich
2018-09-07 14:17 ` Andrew Cooper [this message]
2018-09-07 15:49 ` Jan Beulich
2018-02-27 14:50 ` [PATCH v2 5/5] x86/pv: Implement the failsafe callback using the general path Andrew Cooper
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