Re: [PART1 RFC v2 05/10] KVM: x86: Detect and Initialize AVIC support

From: Suravee Suthikulpanit
Date: Wed Mar 16 2016 - 04:22:25 EST


On 03/16/2016 02:20 PM, Paolo Bonzini wrote:

On 16/03/2016 07:22, Suravee Suthikulpanit wrote:
>This is mainly causing a large number of VMEXIT due to NPF.
Got it, it's here in the manual: "System software is responsible for
setting up a translation in the nested page table granting guest read
and write permissions for accesses to the vAPIC Backing Page in SPA
space. AVIC hardware walks the nested page table to check permissions,
but does not use the SPA address specified in the leaf page table entry.
Instead, AVIC hardware finds this address in the AVIC_BACKING_PAGE
pointer field of the VMCB".

Strictly speaking the address of the 0xFEE00000 translation is
unnecessary and it could be all zeroes, but I suggest that you set up an
APIC access page like Intel does (4k only), using the special memslot.
The AVIC backing page can then point to lapic->regs.

Thanks for the explanation!


Ahh... you are right, this works also. Thanks for the pointer. I'm fixing this, doing some more testing, and cleaning up the code. This has simplify the init logic quite a bit.

Thanks for suggestion,