From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F3F35146580; Wed, 27 Nov 2024 06:47:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732690029; cv=none; b=OHgSyLC7Jmniyi4gqj/3aglKEyH3RCWxy4hqBZ9tkfzb9MNGVsvy/BLMgXrMCo+HwoRB0h2g/ygRj+tjXbwThDn/mQfFHhtEbgLkaKA7AcCdrqglcyF59vDyPOEfiOXcI9UsOrTC2U/YtKHqWdQx7q2RAcctskE5VrEIge9Zpoc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732690029; c=relaxed/simple; bh=IKN3uGXQpsb214rkA0SH3AIlbeF9blKRdxLBQUVz8R8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bkfUua9aAS7t4+eFL+kD3fSXZlRVj9cPSpjgiVatI6ySODPxkTCsczPPjTeyj9wiJbj0qp1sB+pnb5JkYMSVKrsTgZhS69yFfLT+1hZSwDYIw9ANeKjx7qJtygPIzybFWc87pot+mWToNPMJtfS4jlpDegCOItNrb5462m0ox+w= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=LoaidWcdBtqK3iJHkHTC8z3f2py+0XlIgbynqtKiN16Fhv2NzF7TqEp1KnuNmlIMM ZB2oE/qmCg5TIFrmQKdPcehoA9aZAL8gb+zSyPgGGRxoowde070HfpSp2XzPb52XYN ut51pEAVqxNcE0G4QIzpl1v8a0pY7MTJV13g3Gt1tqKEwZM5fz7J+SYrKQgWkQiOmk khYn2ZO0Ihc+p6imEAgTPCWF7owZjGRGHKtaJdaEQEmPfJyo68xbp7cfBKhDmnTWTi J5EKKJVaQE0tr1D0+DV8WQjGLrWtHEml0qu7T1HQL2+fXMz5BuwdP4AZtkiXUbAdaP URB48huTi3dGA== Message-ID: Date: Tue, 26 Nov 2024 22:46:09 -0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 09/27] KVM: VMX: Do not use MAX_POSSIBLE_PASSTHROUGH_MSRS in array definition To: Borislav Petkov Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, andrew.cooper3@citrix.com References: <20241001050110.3643764-1-xin@zytor.com> <20241001050110.3643764-10-xin@zytor.com> <20241126180253.GAZ0YNTdXH1UGeqsu6@fat_crate.local> <20241126200624.GDZ0YqQF96hKZ99x_b@fat_crate.local> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/26/2024 12:06 PM, Borislav Petkov wrote: > On Tue, Nov 26, 2024 at 11:22:45AM -0800, Xin Li wrote: >> It's still far from full in a bitmap on x86-64, but just that the >> existing use of MAX_POSSIBLE_PASSTHROUGH_MSRS tastes bad. > > Far from full? > > It is full: > > static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = { > MSR_IA32_SPEC_CTRL, > MSR_IA32_PRED_CMD, > MSR_IA32_FLUSH_CMD, > MSR_IA32_TSC, > #ifdef CONFIG_X86_64 > MSR_FS_BASE, > MSR_GS_BASE, > MSR_KERNEL_GS_BASE, > MSR_IA32_XFD, > MSR_IA32_XFD_ERR, > #endif > MSR_IA32_SYSENTER_CS, > MSR_IA32_SYSENTER_ESP, > MSR_IA32_SYSENTER_EIP, > MSR_CORE_C1_RES, > MSR_CORE_C3_RESIDENCY, > MSR_CORE_C6_RESIDENCY, > MSR_CORE_C7_RESIDENCY, > }; > > I count 16 here. > > If you need to add more, you need to increment MAX_POSSIBLE_PASSTHROUGH_MSRS. Yes, the most obvious approach is to simply increase MAX_POSSIBLE_PASSTHROUGH_MSRS by the number of MSRs to be added into the array. However I hate to count it myself, especially we have ARRAY_SIZE. > >> A better one? > > Not really. > > You're not explaining why MAX_POSSIBLE_PASSTHROUGH_MSRS becomes 64. > >> Per the definition, a bitmap on x86-64 is an array of 'unsigned long', >> and is at least 64-bit long. >> >> #define DECLARE_BITMAP(name,bits) \ >> unsigned long name[BITS_TO_LONGS(bits)] >> >> It's not accurate and error-prone to use a hard-coded possible size of >> a bitmap, Use ARRAY_SIZE with an overflow build check instead. > > It becomes 64 because a bitmap has 64 bits? Yes, maybe better to name the macro as MAX_ALLOWED_PASSTHROUGH_MSRS? > > Not because you need to add more MSRs to it and thus raise the limit? Right. It triggered me to look at the code further, though, I think the existing code could be written in a better way no matter whether I need to add more MSRs. And whoever wants to add more won't need to increase MAX_POSSIBLE_PASSTHROUGH_MSRS (ofc unless overflow 64). Thanks! Xin