linux-kernel - Re: [PATCH v9 5/7] arm64: kvm: Introduce KVM_ARM_SET_SERROR

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Date:   Wed, 24 Jan 2018 20:06:15 +0000
From:   gengdongjiu <gengdongjiu@...wei.com>
To:     James Morse <james.morse@....com>
CC:     "christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "bp@...en8.de" <bp@...en8.de>,
        "robert.moore@...el.com" <robert.moore@...el.com>,
        "lv.zheng@...el.com" <lv.zheng@...el.com>,
        "corbet@....net" <corbet@....net>,
        "will.deacon@....com" <will.deacon@....com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        Huangshaoyu <huangshaoyu@...wei.com>
Subject: Re: [PATCH v9 5/7] arm64: kvm: Introduce KVM_ARM_SET_SERROR_ESR
 ioctl

Hi James,
   Thanks a lot for your review and comments.

> 
> Hi Dongjiu Geng,
> 
> On 06/01/18 16:02, Dongjiu Geng wrote:
> > The ARM64 RAS SError Interrupt(SEI) syndrome value is specific to the
> > guest and user space needs a way to tell KVM this value. So we add a
> > new ioctl. Before user space specifies the Exception Syndrome Register
> > ESR(ESR), it firstly checks that whether KVM has the capability to set
> > the guest ESR, If has, will set it. Otherwise, nothing to do.
> >
> > For this ESR specifying, Only support for AArch64, not support AArch32.
> 
> After this patch user-space can trigger an SError in the guest. If it wants to migrate the guest, how does the pending SError get migrated?
> 
> I think we need to fix migration first. Andrew Jones suggested using
> KVM_GET/SET_VCPU_EVENTS:
> https://www.spinics.net/lists/arm-kernel/msg616846.html
> 
> Given KVM uses kvm_inject_vabt() on v8.0 hardware too, we should cover systems without the v8.2 RAS Extensions with the same API. I
> think this means a bit to read/write whether SError is pending, and another to indicate the ESR should be set/read.
> CPUs without the v8.2 RAS Extensions can reject pending-SError that had an ESR.

For the CPUs without the v8.2 RAS Extensions, its ESR is always 0, we only can inject a SError with ESR 0 to guest, cannot set its ESR.
About how about to use the KVM_GET/SET_VCPU_EVENTS, I will check the code, and consider your suggestion at the same time. 
The IOCTL KVM_GET/SET_VCPU_EVENTS has been used by X86.

> 
> user-space can then use the 'for migration' calls to make a 'new' SError pending.
> 
> Now that the cpufeature bits are queued, I think this can be split up into two separate series for v4.16-rc1, one to tackle NOTIFY_SEI and
> the associated plumbing. The second for the KVM 'make SError pending' API.

Ok, thanks for your suggestion, will split it.

> 
> 
> > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index
> > 5c7f657..738ae90 100644
> > --- a/arch/arm64/kvm/guest.c
> > +++ b/arch/arm64/kvm/guest.c
> > @@ -277,6 +277,11 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> >  	return -EINVAL;
> >  }
> >
> > +int kvm_arm_set_sei_esr(struct kvm_vcpu *vcpu, u32 *syndrome) {
> > +	return -EINVAL;
> > +}
> 
> Does nothing in the patch that adds the support? This is a bit odd.
> (oh, its hiding in patch 6...)

To make this patch simple and small, I add it in patch 6.

> 
> 
> Thanks,
> 
> James