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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id ch21sm5253715pjb.8.2021.04.22.08.08.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Apr 2021 08:08:01 -0700 (PDT) Date: Thu, 22 Apr 2021 15:07:57 +0000 From: Sean Christopherson To: Colin King Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , kvm@vger.kernel.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH][next] KVM: x86: simplify zero'ing of entry->ebx Message-ID: References: <20210422141129.250525-1-colin.king@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210422141129.250525-1-colin.king@canonical.com> Precedence: bulk List-ID: X-Mailing-List: kernel-janitors@vger.kernel.org On Thu, Apr 22, 2021, Colin King wrote: > From: Colin Ian King > > Currently entry->ebx is being zero'd by masking itself with zero. > Simplify this by just assigning zero, cleans up static analysis > warning. > > Addresses-Coverity: ("Bitwise-and with zero") > Signed-off-by: Colin Ian King > --- > arch/x86/kvm/cpuid.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 57744a5d1bc2..9bcc2ff4b232 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -851,7 +851,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > entry->eax &= SGX_ATTR_DEBUG | SGX_ATTR_MODE64BIT | > SGX_ATTR_PROVISIONKEY | SGX_ATTR_EINITTOKENKEY | > SGX_ATTR_KSS; > - entry->ebx &= 0; > + entry->ebx = 0; I 100% understand the code is funky, but using &= is intentional. ebx:eax holds a 64-bit value that is a effectively a set of feature flags. While the upper 32 bits are extremely unlikely to be used any time soon, if a feature comes along then the correct behavior would be: entry->ebx &= SGX_ATTR_FANCY_NEW_FEATURE; While directly setting entry->ebx would be incorrect. The idea is to set up a future developer for success so that they don't forget to add the "&". TL;DR: I'd prefer to keep this as is, even though it's rather ridiculous. > break; > /* Intel PT */ > case 0x14: > -- > 2.30.2 >