Re: [PATCH v2] KVM: selftest: Enhance handling WRMSR ICR register in x2APIC mode

[Zeng Guang]

On 6/24/2022 4:34 AM, Sean Christopherson wrote:
> +Venkatesh
>
> On Thu, Jun 23, 2022, Chao Gao wrote:
> > On Thu, Jun 23, 2022 at 05:45:11PM +0800, Zeng Guang wrote:
> > > Hardware would directly write x2APIC ICR register instead of software
> > > emulation in some circumstances, e.g when Intel IPI virtualization is
> > > enabled. This behavior requires normal reserved bits checking to ensure
> > > them input as zero, otherwise it will cause #GP. So we need mask out
> > > those reserved bits from the data written to vICR register.
> > OK. One open is:
> >
> > Current KVM doesn't emulate this #GP. Is there any historical reason?
> > if no, we will fix KVM and add some tests to verify this #GP is
> > correctly emulated.
> It's a bug.  There are patches posted[*], but they need to be refreshed to fix a
> rebase goof.
>
> Venkatesh, are you planning on sending a v3 soonish?
>
> [*] https://lore.kernel.org/all/20220525173933.1611076-1-venkateshs@xxxxxxxxxxxx

This patch set doesn't emulate hardware behavior precisely . Actually 
#GP will
happen only if any of reserved bit ( bit[31:20],bit[17:16],bit[13]) is 
1-setting
in x2apic mode. Other bits including bit[12] won't have any impact. For 
xapic
mode, it doesn't have this restriction.