From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Morse Subject: Re: [PATCH RESEND v4 2/2] arm/arm64: KVM: Add KVM_GET/SET_VCPU_EVENTS Date: Fri, 15 Jun 2018 16:57:48 +0100 Message-ID: <9e5be3fe-e6df-ca56-5eab-9ab7e18d9a99@arm.com> References: <1528487320-2873-1-git-send-email-gengdongjiu@huawei.com> <1528487320-2873-3-git-send-email-gengdongjiu@huawei.com> <45e94aae-ed9f-1fb7-f10e-d95c2f969ddd@arm.com> <6887237f-d252-5b9e-02cb-5a44fef27080@arm.com> <2455dc33-ae8d-79e6-e915-4181050e1e65@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <2455dc33-ae8d-79e6-e915-4181050e1e65@huawei.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: gengdongjiu Cc: rkrcmar@redhat.com, corbet@lwn.net, christoffer.dall@arm.com, marc.zyngier@arm.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org List-Id: linux-acpi@vger.kernel.org Hi gengdongjiu, On 12/06/18 16:48, gengdongjiu wrote: > On 2018/6/12 23:29, James Morse wrote: >> On 12/06/18 15:50, gengdongjiu wrote: >>> On 2018/6/11 21:36, James Morse wrote: >>>> On 08/06/18 20:48, Dongjiu Geng wrote: >>>>> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h >>>>> index caae484..c3e6975 100644 >>>>> --- a/arch/arm/include/uapi/asm/kvm.h >>>>> +++ b/arch/arm/include/uapi/asm/kvm.h >>>>> @@ -124,6 +124,18 @@ struct kvm_sync_regs { >>>>> struct kvm_arch_memory_slot { >>>>> }; >>>>> >>>>> +/* for KVM_GET/SET_VCPU_EVENTS */ >>>>> +struct kvm_vcpu_events { >>>>> + struct { >>>>> + __u8 serror_pending; >>>>> + __u8 serror_has_esr; >>>>> + /* Align it to 8 bytes */ >>>>> + __u8 pad[6]; >>>>> + __u64 serror_esr; >>>>> + } exception; >>>>> + __u32 reserved[12]; >>>>> +}; >>>>> + >>>> >>>> You haven't defined __KVM_HAVE_VCPU_EVENTS for 32bit, so presumably this struct >>>> will never be used. Why is it here? >> >>> if not add it for 32 bits. the 32 arm platform will build Fail, whether you have good >>> idea to avoid this Failure if not add this struct for the 32 bit? >> >> How does this 32bit code build without this patch? >> If do you provide the struct, how will that code build with older headers? >> >> As far as I can see, this is what the __KVM_HAVE_VCPU_EVENTS define is for. >> >> This should be both, or neither. Having just the struct is useless. > It because the caller of kvm_arm_vcpu_get/set_events() is in "virt/kvm/arm/arm.c". > the virt/kvm/arm/arm.c will used by both arm64 and arm. > so It needs to add kvm_arm_vcpu_get/set_events() for the 32 bits, however, kvm_arm_vcpu_get/set_events() will directly return, So you are adding a uapi struct that user-space can't actually use, to avoid a kernel build-error. Fine, it just looks really strange. 32bit user-space shouldn't try to call this as check-extension reports it as not present. If it does, it gets -EINVAL back, which is also the default for kvm_arch_vcpu_ioctl(). Thanks, James