* reading IOPL
@ 2012-05-03 16:07 Jan Beulich
2012-05-03 17:22 ` Konrad Rzeszutek Wilk
0 siblings, 1 reply; 3+ messages in thread
From: Jan Beulich @ 2012-05-03 16:07 UTC (permalink / raw)
To: xen-devel
Both Linux and Xen offer only ways to set the IOPL. While on native Linux
this is not a problem since user mode code can read the IOPL by inspecting
EFLAGS, on Xen this would always yield zero.
Now X folks appear to be using save-modify-restore cycles in some newer
code, and this obviously breaks under Xen, as they would restore IOPL 0
even when IOPL 3 was in effect before.
Since the only way to read the IOPL is xc_vcpu_getcontext() (i.e.
XEN_DOMCTL_getvcpucontext), I wonder whether we shouldn't add
e.g. a "get" counterpart to PHYSDEVOP_set_iopl.
Or am I overlooking some other access mechanism?
Jan
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: reading IOPL
2012-05-03 16:07 reading IOPL Jan Beulich
@ 2012-05-03 17:22 ` Konrad Rzeszutek Wilk
2012-05-04 7:09 ` Jan Beulich
0 siblings, 1 reply; 3+ messages in thread
From: Konrad Rzeszutek Wilk @ 2012-05-03 17:22 UTC (permalink / raw)
To: Jan Beulich; +Cc: xen-devel
On Thu, May 03, 2012 at 05:07:04PM +0100, Jan Beulich wrote:
> Both Linux and Xen offer only ways to set the IOPL. While on native Linux
> this is not a problem since user mode code can read the IOPL by inspecting
> EFLAGS, on Xen this would always yield zero.
>
> Now X folks appear to be using save-modify-restore cycles in some newer
> code, and this obviously breaks under Xen, as they would restore IOPL 0
This is in the KMS drivers or in the user-land Xorg?
> even when IOPL 3 was in effect before.
>
> Since the only way to read the IOPL is xc_vcpu_getcontext() (i.e.
> XEN_DOMCTL_getvcpucontext), I wonder whether we shouldn't add
> e.g. a "get" counterpart to PHYSDEVOP_set_iopl.
>
> Or am I overlooking some other access mechanism?
>
> Jan
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: reading IOPL
2012-05-03 17:22 ` Konrad Rzeszutek Wilk
@ 2012-05-04 7:09 ` Jan Beulich
0 siblings, 0 replies; 3+ messages in thread
From: Jan Beulich @ 2012-05-04 7:09 UTC (permalink / raw)
To: Konrad Rzeszutek Wilk; +Cc: xen-devel
>>> On 03.05.12 at 19:22, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> On Thu, May 03, 2012 at 05:07:04PM +0100, Jan Beulich wrote:
>> Both Linux and Xen offer only ways to set the IOPL. While on native Linux
>> this is not a problem since user mode code can read the IOPL by inspecting
>> EFLAGS, on Xen this would always yield zero.
>>
>> Now X folks appear to be using save-modify-restore cycles in some newer
>> code, and this obviously breaks under Xen, as they would restore IOPL 0
>
> This is in the KMS drivers or in the user-land Xorg?
Userland code (as explained above).
Jan
>> even when IOPL 3 was in effect before.
>>
>> Since the only way to read the IOPL is xc_vcpu_getcontext() (i.e.
>> XEN_DOMCTL_getvcpucontext), I wonder whether we shouldn't add
>> e.g. a "get" counterpart to PHYSDEVOP_set_iopl.
>>
>> Or am I overlooking some other access mechanism?
>>
>> Jan
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2012-05-04 7:09 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2012-05-03 16:07 reading IOPL Jan Beulich
2012-05-03 17:22 ` Konrad Rzeszutek Wilk
2012-05-04 7:09 ` Jan Beulich
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