linux-kernel - Re: [PATCH v2 03/10] KVM: arm/arm64: vgic-its: Improve error reporting on device table save

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Date:   Sat, 14 Oct 2017 08:06:25 -0700
From:   Christoffer Dall <cdall@...aro.org>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, marc.zyngier@....com,
        peter.maydell@...aro.org, andre.przywara@....com,
        wanghaibin.wang@...wei.com, wu.wubin@...wei.com
Subject: Re: [PATCH v2 03/10] KVM: arm/arm64: vgic-its: Improve error
 reporting on device table save

On Sat, Oct 14, 2017 at 10:52:45AM +0200, Auger Eric wrote:
> Hi Christoffer,
> 
> On 13/10/2017 19:56, Christoffer Dall wrote:
> > On Fri, Oct 13, 2017 at 04:22:25PM +0200, Auger Eric wrote:
> >> Hi,
> >>
> >> On 13/10/2017 15:16, Christoffer Dall wrote:
> >>> On Wed, Sep 27, 2017 at 03:28:33PM +0200, Eric Auger wrote:
> >>>> At the moment the device table save() returns -EINVAL if
> >>>> vgic_its_check_id() fails to return the gpa of the entry
> >>>> associated to the device/collection id. Let vgic_its_check_id()
> >>>> return an int instead of a bool and return a more precised
> >>>> error value:
> >>>> - EINVAL in case the id is out of range
> >>>> - EFAULT if the gpa is not provisionned or is not valid
> >>>>
> >>>
> >>> This is just to ease debugging, yes?
> >>
> >> I understood user-space should be able to discriminate between bad guest
> >> programming and values corrupted by the userspace (regs for instance).
> >> In first case QEMU should not abort. In latter case it should abort.
> > 
> > So what is userspace supposed to do in the first case?
> 
> I was referring to https://www.spinics.net/lists/kvm/msg148791.html.
> QEMU is supposed to write a message in that case but not cause an abort().
> 
> This is what is actually implemented on QEMU side. In case the ioctl
> returns -EFAULT, we don't abort but simply warn. However at the moment
> we return -EINVAL in some circumstances where - I think - we should
> return -EFAULT. Hence this patch attempting to be more precise on the
> cause of the failure instead of abruptly returning -EINVAL here.
> 

ok, thanks makes sense.  Thanks for sharing the background.

-Christoffer