Re: [PATCH v7 02/12] KVM: arm64: Use kvm_arch_flush_remote_tlbs()

From: Marc Zyngier <maz@kernel.org>
To: Raghavendra Rao Ananta <rananta@google.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Huacai Chen <chenhuacai@kernel.org>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Anup Patel <anup@brainfault.org>,
	Atish Patra <atishp@atishpatra.org>,
	Jing Zhang <jingzhangos@google.com>,
	Reiji Watanabe <reijiw@google.com>,
	Colton Lewis <coltonlewis@google.com>,
	David Matlack <dmatlack@google.com>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [PATCH v7 02/12] KVM: arm64: Use kvm_arch_flush_remote_tlbs()
Date: Thu, 27 Jul 2023 11:25:25 +0100	[thread overview]
Message-ID: <87tttpr6qy.wl-maz@kernel.org> (raw)
In-Reply-To: <20230722022251.3446223-3-rananta@google.com>

On Sat, 22 Jul 2023 03:22:41 +0100,
Raghavendra Rao Ananta <rananta@google.com> wrote:
> 
> Stop depending on CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL and opt to
> standardize on kvm_arch_flush_remote_tlbs() since it avoids
> duplicating the generic TLB stats across architectures that implement
> their own remote TLB flush.
> 
> This adds an extra function call to the ARM64 kvm_flush_remote_tlbs()
> path, but that is a small cost in comparison to flushing remote TLBs.

Well, there is no such thing as a "remote TLB" anyway. We either have
a non-shareable or inner-shareable invalidation. The notion of remote
would imply that we track who potentially has a TLB, which we
obviously don't.

More x86 nonsense...

>
> In addition, instead of just incrementing remote_tlb_flush_requests
> stat, the generic interface would also increment the
> remote_tlb_flush stat.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 3 +++
>  arch/arm64/kvm/Kconfig            | 1 -
>  arch/arm64/kvm/mmu.c              | 6 +++---
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 8b6096753740..7281222f24ef 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1111,6 +1111,9 @@ int __init kvm_set_ipa_limit(void);
>  #define __KVM_HAVE_ARCH_VM_ALLOC
>  struct kvm *kvm_arch_alloc_vm(void);
>  
> +#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS
> +int kvm_arch_flush_remote_tlbs(struct kvm *kvm);

See my earlier comment about making this prototype global.

	M.

-- 
Without deviation from the norm, progress is not possible.

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