linux-kernel - Re: [PATCH v2 06/12] RISC-V: KVM: Implement kvm_arch_flush_remote_tlbs

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Message-ID: <422c5677-48d1-41be-b128-595829c27167@linux.dev>
Date: Fri, 13 Jun 2025 17:43:51 -0700
From: Atish Patra <atish.patra@...ux.dev>
To: Anup Patel <apatel@...tanamicro.com>
Cc: Palmer Dabbelt <palmer@...belt.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Alexandre Ghiti <alex@...ti.fr>,
 Andrew Jones <ajones@...tanamicro.com>, Anup Patel <anup@...infault.org>,
 kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/12] RISC-V: KVM: Implement
 kvm_arch_flush_remote_tlbs_range()


On 6/12/25 11:57 PM, Anup Patel wrote:
> The kvm_arch_flush_remote_tlbs_range() expected by KVM core can be
> easily implemented for RISC-V using kvm_riscv_hfence_gvma_vmid_gpa()
> hence provide it.
>
> Also with kvm_arch_flush_remote_tlbs_range() available for RISC-V, the
> mmu_wp_memory_region() can happily use kvm_flush_remote_tlbs_memslot()
> instead of kvm_flush_remote_tlbs().
>
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
>   arch/riscv/include/asm/kvm_host.h | 2 ++
>   arch/riscv/kvm/mmu.c              | 2 +-
>   arch/riscv/kvm/tlb.c              | 8 ++++++++
>   3 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index ff1f76d6f177..6162575e2177 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -43,6 +43,8 @@
>   	KVM_ARCH_REQ_FLAGS(5, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>   #define KVM_REQ_STEAL_UPDATE		KVM_ARCH_REQ(6)
>   
> +#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
> +
>   #define KVM_HEDELEG_DEFAULT		(BIT(EXC_INST_MISALIGNED) | \
>   					 BIT(EXC_BREAKPOINT)      | \
>   					 BIT(EXC_SYSCALL)         | \
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 29f1bd853a66..a5387927a1c1 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -344,7 +344,7 @@ static void gstage_wp_memory_region(struct kvm *kvm, int slot)
>   	spin_lock(&kvm->mmu_lock);
>   	gstage_wp_range(kvm, start, end);
>   	spin_unlock(&kvm->mmu_lock);
> -	kvm_flush_remote_tlbs(kvm);
> +	kvm_flush_remote_tlbs_memslot(kvm, memslot);
>   }
>   
>   int kvm_riscv_gstage_ioremap(struct kvm *kvm, gpa_t gpa,
> diff --git a/arch/riscv/kvm/tlb.c b/arch/riscv/kvm/tlb.c
> index da98ca801d31..f46a27658c2e 100644
> --- a/arch/riscv/kvm/tlb.c
> +++ b/arch/riscv/kvm/tlb.c
> @@ -403,3 +403,11 @@ void kvm_riscv_hfence_vvma_all(struct kvm *kvm,
>   	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE_VVMA_ALL,
>   			    KVM_REQ_HFENCE_VVMA_ALL, NULL);
>   }
> +
> +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t gfn, u64 nr_pages)
> +{
> +	kvm_riscv_hfence_gvma_vmid_gpa(kvm, -1UL, 0,
> +				       gfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT,
> +				       PAGE_SHIFT);
> +	return 0;
> +}

LGTM. However, I noticed that kvm_flush_remote_tlbs_range doesn't 
increment remote_tlb_flush_requests/remote_tlb_flush stat counter.

So we would be losing those stats here. Do you know if there is a 
specific reason behind not supporting the stat counters in the *tlbs_range
function ?

Otherwise,
Reviewed-by: Atish Patra <atishp@...osinc.com>