Re: [PATCH 5/6] LoongArch: KVM: Add remote tlb flushing support

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Local TLB flush requests via KVM_REQ_TLB_FLUSH are silently ignored when cpu_has_guestid is true.
--

--- Patch [5]: [PATCH 5/6] LoongArch: KVM: Add remote tlb flushing support ---
commit 8224c08441c8eee94923d3771b8015f38a7278ab
Author: Bibo Mao <maobibo@loongson.cn>

LoongArch: KVM: Add remote tlb flushing support

This commit introduces remote TLB flushing support by queueing a TLB
invalidation for each CPU to perform on the next vCPU load. It adds a
tlb_flush_pending cpumask and updates the vmid index when scheduled on
a physical CPU, while keeping the vpid index unchanged.

[ ... ]

> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 20c207d80e31a..19c81ae8941a9 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -210,7 +210,12 @@ static int kvm_check_requests(struct kvm_vcpu *vcpu)
>  		return RESUME_GUEST;
>  
>  	if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu))
> -		vcpu->arch.vpid = 0;  /* Drop vpid for this vCPU */
> +		/*
> +		 * vpid need the same with vmid if vpid is not separated
> +		 * with vmid
> +		 */
> +		if (!cpu_has_guestid)
> +			vcpu->arch.vpid = 0;  /* Drop vpid for this vCPU */

[Severity: High]
Does this silently ignore local TLB flush requests when cpu_has_guestid is
true?

If a local KVM_REQ_TLB_FLUSH is made, for example by kvm_map_page() in
arch/loongarch/kvm/mmu.c when upgrading to a huge page, kvm_check_request()
will clear the request bit here.

However, if cpu_has_guestid is true, the VPID is not dropped. Because this
is a local flush, the tlb_flush_pending cpumask is not set globally, meaning
kvm_check_vmid() will not drop the VMID either.

Will this cause the local TLB flush to be completely lost, potentially
leading to an infinite page fault loop if the guest hits a stale invalid
TLB entry on hardware with a page table walker?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260727072109.2151675-1-maobibo@loongson.cn?part=5