From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH v5 1/2] KVM: Switch 'requests' to be 64-bit (explicitly) Date: Wed, 18 Jul 2018 17:34:29 +0200 Message-ID: <20180718153429.GC6348@flask> References: <1531214840-24686-1-git-send-email-karahmed@amazon.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini To: KarimAllah Ahmed Return-path: Content-Disposition: inline In-Reply-To: <1531214840-24686-1-git-send-email-karahmed@amazon.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 2018-07-10 11:27+0200, KarimAllah Ahmed: > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to > use the size of "requests" instead of the hard-coded '32'. > > That gives us a bit more room again for arch-specific requests as we > already ran out of space for x86 due to the hard-coded check. > > The only exception here is ARM32 as it is still 32-bits. What do you mean? I think we're just going to slow down kvm_request_pending() on 32 bit architectures. > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: kvm@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Reviewed-by: Jim Mattson > Signed-off-by: KarimAllah Ahmed > --- > v1 -> v2: > - Use FIELD_SIZEOF > --- > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > @@ -130,7 +130,7 @@ static inline bool is_error_page(struct page *page) > #define KVM_REQUEST_ARCH_BASE 8 Now that the base is easily moveable, we could also lower it to 4 and get few more arch flags. Bumping requests to 64 bits is probably inevitable and this patch looks good. In v4, you have proposed the bitmap-array solution that would easily allow more than 64 requests -- was the problem that possible implementations of kvm_request_pending were not as efficient for current amount of requests? Thanks. > #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \ > - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \ > + BUILD_BUG_ON((unsigned)(nr) >= (FIELD_SIZEOF(struct kvm_vcpu, requests) * 8) - KVM_REQUEST_ARCH_BASE); \ > (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \ > }) > #define KVM_ARCH_REQ(nr) KVM_ARCH_REQ_FLAGS(nr, 0)