Re: [PATCH RESEND v4 2/2] arm/arm64: KVM: Add KVM_GET/SET_VCPU_EVENTS

From: gengdongjiu <gengdongjiu@huawei.com>
To: James Morse <james.morse@arm.com>
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>
Subject: Re: [PATCH RESEND v4 2/2] arm/arm64: KVM: Add KVM_GET/SET_VCPU_EVENTS
Date: Tue, 12 Jun 2018 23:48:16 +0800	[thread overview]
Message-ID: <2455dc33-ae8d-79e6-e915-4181050e1e65@huawei.com> (raw)
In-Reply-To: <6887237f-d252-5b9e-02cb-5a44fef27080@arm.com>


On 2018/6/12 23:29, James Morse wrote:
> Hi gengdongjiu,
> 
> 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:
>>>> For the migrating VMs, user space may need to know the exception
>>>> state. For example, in the machine A, KVM make an SError pending,
>>>> when migrate to B, KVM also needs to pend an SError.
>>>>
>>>> This new IOCTL exports user-invisible states related to SError.
>>>> Together with appropriate user space changes, user space can get/set
>>>> the SError exception state to do migrate/snapshot/suspend.
> 
> 
>>>> 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,

I attached the build erros below:
https://lkml.org/lkml/2018/6/4/918
https://lkml.org/lkml/2018/6/4/873


[..]
I will continue check below comments, thanks