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Date:   Wed, 22 Mar 2023 10:52:01 -0700
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Subject: Re: [PATCH v5 05/34] x86/traps: export external_interrupt() for VMX
 IRQ reinjection
From:   Sean Christopherson <seanjc@google.com>
To:     Xin Li <xin3.li@intel.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org,
        andrew.cooper3@citrix.com, pbonzini@redhat.com,
        ravi.v.shankar@intel.com
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On Mon, Mar 06, 2023, Xin Li wrote:
> To eliminate dispatching IRQ through the IDT, export external_interrupt()
> for VMX IRQ reinjection.
> 
> Tested-by: Shan Kang <shan.kang@intel.com>
> Signed-off-by: Xin Li <xin3.li@intel.com>
> ---
>  arch/x86/include/asm/traps.h |  2 ++
>  arch/x86/kernel/traps.c      | 14 ++++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
> index 46f5e4e2a346..da4c21ed68b4 100644
> --- a/arch/x86/include/asm/traps.h
> +++ b/arch/x86/include/asm/traps.h
> @@ -56,4 +56,6 @@ void __noreturn handle_stack_overflow(struct pt_regs *regs,
>  	void f (struct pt_regs *regs)
>  typedef DECLARE_SYSTEM_INTERRUPT_HANDLER((*system_interrupt_handler));
>  
> +int external_interrupt(struct pt_regs *regs, unsigned int vector);
> +
>  #endif /* _ASM_X86_TRAPS_H */
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 31ad645be2fb..cebba1f49e19 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -1540,6 +1540,20 @@ int external_interrupt(struct pt_regs *regs, unsigned int vector)
>  	return 0;
>  }
>  
> +#if IS_ENABLED(CONFIG_KVM_INTEL)
> +/*
> + * KVM VMX reinjects IRQ on its current stack, it's a sync call
> + * thus the values in the pt_regs structure are not used in
> + * executing IRQ handlers, except cs.RPL and flags.IF, which
> + * are both always 0 in the VMX IRQ reinjection context.
> + *
> + * However, the pt_regs structure is sometimes used in stack
> + * dump, e.g., show_regs(). So let the caller, i.e., KVM VMX
> + * decide how to initialize the input pt_regs structure.
> + */
> +EXPORT_SYMBOL_GPL(external_interrupt);
> +#endif

If the x86 maintainers don't object, I would prefer this to be squashed with the
actual KVM usage, that way discussions on exactly what the exported API should be
can be contained in a single thread.