Re: [PATCH for-4.14 2/8] x86/hvm: don't force vCPU 0 for IRQ 0 when using fixed destination mode

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.06.2020 17:56, Roger Pau Monne wrote:
> When the IO APIC pin mapped to the ISA IRQ 0 has been configured to
> use fixed delivery mode do not forcefully route interrupts to vCPU 0,
> as the OS might have setup those interrupts to be injected to a
> different vCPU, and injecting to vCPU 0 can cause the OS to miss such
> interrupts or errors to happen due to unexpected vectors being
> injected on vCPU 0.
> 
> In order to fix remove such handling altogether for fixed destination
> mode pins and just inject them according to the data setup in the
> IO-APIC entry.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Technically
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

I wonder though why this was done in the first place - it very much
feels like a workaround for certain guest behavior, and hence
getting rid of it may mean a certain risk of regressions. Not a
very good point in time to make risky changes ...

Jan