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Re: [PATCH] x86/fred: Send an EVENT_CHECK IPI on exit from NMI
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 24 Jun 2026 16:09:07 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 24 Jun 2026 15:09:28 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24/06/2026 3:47 pm, Jan Beulich wrote:
> On 24.06.2026 16:23, Andrew Cooper wrote:
>> --- a/xen/arch/x86/x86_64/entry-fred.S
>> +++ b/xen/arch/x86/x86_64/entry-fred.S
>> @@ -20,6 +20,12 @@ FUNC(entry_FRED_R3, 4096)
>> GET_STACK_END(14)
>> movq STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
>>
>> + /* NMIs need special handling on return to guest. */
>> + movzbl UREGS_ss + 6(%rsp), %eax
>> + and $0xf, %eax
>> + cmp $X86_ET_NMI, %al
>> + je nmi_exit_to_guest
>> +
>> jmp test_all_events
> Actually, how about shrinking this to just
>
> test %al, %al
> jnz nmi_exit_to_guest
>
> by having entry_from_pv() return a boolean?
I considered that, and dismissed it.
It involve changing large chunks of traps.c (simply to compile) and puts
far more than 4 instructions of logic onto the common path.
~Andrew
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