linux-kernel - Re: [PATCH] riscv: KVM: Remove unnecessary vcpu kick

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Message-ID: <20250219-badec60b9b12834cf534dcbf@orel>
Date: Wed, 19 Feb 2025 09:36:05 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: BillXiang <xiangwencheng@...xincomputing.com>
Cc: anup@...infault.org, kvm-riscv@...ts.infradead.org, 
	kvm@...r.kernel.org, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	atishp@...shpatra.org, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu
Subject: Re: [PATCH] riscv: KVM: Remove unnecessary vcpu kick

On Wed, Feb 19, 2025 at 09:54:26AM +0800, BillXiang wrote:
> Thank you Andrew Jones, forgive my errors in the last email.

>From here down is all exactly the same as your first email, which I
already completely replied to.

> I'm wondering whether it's necessary to kick the virtual hart
> after writing to the vsfile of IMSIC.
> From my understanding, writing to the vsfile should directly
> forward the interrupt as MSI to the virtual hart. This means that
> an additional kick should not be necessary, as it would cause the
> vCPU to exit unnecessarily and potentially degrade performance.
> I've tested this behavior in QEMU, and it seems to work perfectly
> fine without the extra kick.
> Would appreciate any insights or confirmation on this!
> Best regards.
> 
> Signed-off-by: BillXiang <xiangwencheng@...xincomputing.com>
> ---
>  arch/riscv/kvm/aia_imsic.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
> index a8085cd8215e..29ef9c2133a9 100644
> --- a/arch/riscv/kvm/aia_imsic.c
> +++ b/arch/riscv/kvm/aia_imsic.c
> @@ -974,7 +974,6 @@ int kvm_riscv_vcpu_aia_imsic_inject(struct kvm_vcpu *vcpu,
>  
>  	if (imsic->vsfile_cpu >= 0) {
>  		writel(iid, imsic->vsfile_va + IMSIC_MMIO_SETIPNUM_LE);
> -		kvm_vcpu_kick(vcpu);
>  	} else {
>  		eix = &imsic->swfile->eix[iid / BITS_PER_TYPE(u64)];
>  		set_bit(iid & (BITS_PER_TYPE(u64) - 1), eix->eip);
> -- 
> 2.46.2