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([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.googlemail.com with ESMTPSA id k2-20020a170906128200b0098e2eaec394sm904339ejb.101.2023.07.18.04.41.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Jul 2023 04:41:10 -0700 (PDT) Message-ID: Date: Tue, 18 Jul 2023 13:41:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Content-Language: en-US To: Maxim Levitsky , kvm@vger.kernel.org Cc: "H. Peter Anvin" , Sean Christopherson , linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Dave Hansen , x86@kernel.org, Borislav Petkov References: <20230718091310.119672-1-mlevitsk@redhat.com> <20230718091310.119672-2-mlevitsk@redhat.com> From: Paolo Bonzini Subject: Re: [PATCH 1/3] KVM: x86: VMX: __kvm_apic_update_irr must update the IRR atomically In-Reply-To: <20230718091310.119672-2-mlevitsk@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/18/23 11:13, Maxim Levitsky wrote: > + irr_val = READ_ONCE(*((u32 *)(regs + APIC_IRR + i * 0x10))); Let's separate out the complicated arithmetic, as it recurs below too: u32 *p_irr = (u32 *)(regs + APIC_IRR + i * 0x10); > + while (!try_cmpxchg(((u32 *)(regs + APIC_IRR + i * 0x10)), > + &irr_val, irr_val | pir_val)); > + > prev_irr_val = irr_val; > - irr_val |= xchg(&pir[i], 0); > - *((u32 *)(regs + APIC_IRR + i * 0x10)) = irr_val; > - if (prev_irr_val != irr_val) { > - max_updated_irr = > - __fls(irr_val ^ prev_irr_val) + vec; > - } > + irr_val |= pir_val; > + > + if (prev_irr_val != irr_val) > + max_updated_irr = __fls(irr_val ^ prev_irr_val) + vec; We can write this a bit more cleanly too, and avoid unnecessary try_cmpxchg too: prev_irr_val = irr_val; do irr_val = prev_irr_val | pir_val; while (prev_irr_val != irr_val && !try_cmpxchg(p_irr, &prev_irr_val, irr_val)); if (prev_irr_val != irr_val) max_updated_irr = __fls(irr_val ^ prev_irr_val) + vec; If this looks okay to you, I'll queue the patches for -rc3 and also Cc them for inclusion in stable kernels. Paolo