Re: [PATCH] x86, apic: Enable x2APIC physical when cpu < 256 native

[Ingo Molnar <mingo@kernel.org>]

* Youquan Song <youquan.song@linux.intel.com> wrote:

> > In order to make sure the patch without involving unexpected issues beyond
> > I can understand, I will confirm with our expert about it.
> > 
> > so please pend the patch going to mainline. If the patch can move on, I
> > think I will also provide other patch changing, like direct EOI.
> 
> Hi Yinghai and Ingo,
> 
> I have confirmed with our experts about it. x2APIC without interrupt
> remapping is not architecture and no guarantee it will work in future.
> 
> What's more, there are some words in SDM3, 
> 10.12.7 Initialization by System
> Software Routing of device interrupts to local APIC units operating in
> x2APIC mode requires use of the interrupt-remapping architecture
> specified in the Intel Virtualization Technology for Directed I/O,
> Revision 1.3. Because of this, BIOS must enumerate support for and
> software must enable this interrupt remapping with Extended Interrupt
> Mode Enabled before it enabling x2APIC mode in the local APIC units.
> 
> Ingo, please drop the patch in -tip tree.
> 3d1acb49d22fbbae96524040e9e2d4cbbb3adbef "x86/apic: Enable x2APIC
> physical mode on native hardware too, when there are fewer than 256 
> CPUs" 

Ok, dropped it - it was still the tail commit.

> Sorry for making fuss here and it is my fault.

No problem - you might want to send another patch adding some comments to 
the code, explaining why we don't switch to physical mode, quoting from 
the SDM and so.

Thanks,

	Ingo