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Date:   Fri, 9 Jun 2023 11:06:02 +0200
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Subject: Re: [PATCH mm-unstable v2 09/10] kvm/x86: add
 kvm_arch_test_clear_young()
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To:     Yu Zhao <yuzhao@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Alistair Popple <apopple@nvidia.com>,
        Anup Patel <anup@brainfault.org>,
        Ben Gardon <bgardon@google.com>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Fabiano Rosas <farosas@linux.ibm.com>,
        Gaosheng Cui <cuigaosheng1@huawei.com>,
        Gavin Shan <gshan@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        James Morse <james.morse@arm.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Jonathan Corbet <corbet@lwn.net>,
        Marc Zyngier <maz@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michael Larabel <michael@michaellarabel.com>,
        Mike Rapoport <rppt@kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Oliver Upton <oliver.upton@linux.dev>,
        Paul Mackerras <paulus@ozlabs.org>,
        Peter Xu <peterx@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Thomas Huth <thuth@redhat.com>, Will Deacon <will@kernel.org>,
        Zenghui Yu <yuzenghui@huawei.com>, kvmarm@lists.linux.dev,
        kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
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References: <20230526234435.662652-1-yuzhao@google.com>
 <20230526234435.662652-10-yuzhao@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <20230526234435.662652-10-yuzhao@google.com>
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On 5/27/23 01:44, Yu Zhao wrote:
> +#define kvm_arch_has_test_clear_young kvm_arch_has_test_clear_young
> +static inline bool kvm_arch_has_test_clear_young(void)
> +{
> +	return IS_ENABLED(CONFIG_X86_64) &&
> +	       (!IS_REACHABLE(CONFIG_KVM) || (tdp_mmu_enabled && shadow_accessed_mask));
> +}

I don't think you need IS_REACHABLE(CONFIG_KVM) here, it would be a bug 
if this is called from outside KVM code.

Maybe make it a BUILD_BUG_ON?

Paolo