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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id r18sm3462688wrj.50.2020.10.29.00.08.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Oct 2020 00:08:49 -0700 (PDT) Subject: Re: [PATCH 0/3] KVM: x86/mmu: Add macro for hugepage GFN mask To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon References: <20201027214300.1342-1-sean.j.christopherson@intel.com> <80038ae1-d603-dc22-1997-1ad7da0a936d@redhat.com> <20201028152948.GA7584@linux.intel.com> From: Paolo Bonzini Message-ID: Date: Thu, 29 Oct 2020 08:08:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201028152948.GA7584@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/10/20 16:29, Sean Christopherson wrote: > The naming and usage also aligns with the kernel, which defines PAGE, PMD and > PUD masks, and has near identical usage patterns. > > #define PAGE_SIZE (_AC(1,UL) << PAGE_SHIFT) > #define PAGE_MASK (~(PAGE_SIZE-1)) > > #define PMD_PAGE_SIZE (_AC(1, UL) << PMD_SHIFT) > #define PMD_PAGE_MASK (~(PMD_PAGE_SIZE-1)) > > #define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT) > #define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1)) Well, PAGE_MASK is also one of my pet peeves for Linux. At least I am consistent. :) >> and of course if you're debugging it you have to >> look closer and check if it's really "x & -y" or "x & ~y", but at least >> in normal cursory code reading that's how it works for me. > > IMO, "x & -y" has a higher barrier to entry, especially when the kernel's page > masks uses "x & ~(y - 1))". But, my opinion is definitely colored by my > inability to read two's-complement on the fly. Fair enough. What about having instead #define KVM_HPAGE_GFN_BASE(gfn, level) \ (x & ~(KVM_PAGES_PER_HPAGE(gfn) - 1)) #define KVM_HPAGE_GFN_INDEX(gfn, level) \ (x & (KVM_PAGES_PER_HPAGE(gfn) - 1)) ? Paolo