Re: [PATCH 13/14] KVM: Clarify KVM_{SET,GET}_ONE_REG error code documentation

From: Dave Martin <Dave.Martin@arm.com>
To: Andrew Jones <drjones@redhat.com>
Cc: Okamoto Takayuki <tokamoto@jp.fujitsu.com>,
	Christoffer Dall <cdall@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Zhang Lei <zhang.lei@jp.fujitsu.com>,
	Julien Grall <julien.grall@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 13/14] KVM: Clarify KVM_{SET,GET}_ONE_REG error code documentation
Date: Tue, 16 Apr 2019 13:42:43 +0100	[thread overview]
Message-ID: <20190416124243.GP3567@e103592.cambridge.arm.com> (raw)
In-Reply-To: <20190415152132.avwkmmuwolh7juhy@kamzik.brq.redhat.com>

On Mon, Apr 15, 2019 at 05:21:32PM +0200, Andrew Jones wrote:
> On Fri, Apr 12, 2019 at 05:28:17PM +0100, Dave Martin wrote:
> > The current error code documentation for KVM_GET_ONE_REG and
> > KVM_SET_ONE_REG could be read as implying that all architectures
> > implement these error codes, or that KVM guararntees which error
> 
> guarantees
> 
> > code is returned in a particular situation.
> > 
> > Because this is not really the case, this patch waters down the
> > documentation explicitly to remove such guarantees.
> > 
> > EPERM is marked as arm64-specific, since for now arm64 really is
> > the only architecture that yields this error code for the
> > finalization-required case.  Keeping this as a distinct error code
> > is useful however for debugging due to the statefulness of the API
> > in this instance.
> > 
> > No functional change.
> > 
> > Suggested-by: Andrew Jones <drjones@redhat.com>
> > Fixes: 395f562f2b4c ("KVM: Document errors for KVM_GET_ONE_REG and KVM_SET_ONE_REG")
> > Fixes: 50036ad06b7f ("KVM: arm64/sve: Document KVM API extensions for SVE")
> > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > ---
> >  Documentation/virtual/kvm/api.txt | 14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index b115b23..74c51c7 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1873,8 +1873,10 @@ Parameters: struct kvm_one_reg (in)
> >  Returns: 0 on success, negative value on failure
> >  Errors:
> >    ENOENT:   no such register
> > -  EPERM:    register access forbidden for architecture-dependent reasons
> > -  EINVAL:   other errors, such as bad size encoding for a known register
> > +  EINVAL:   invalid register ID, or no such register
> > +  EPERM:    (arm64) register access not allowed before vcpu finalization
> > +(These error codes are indicative only: do not rely on a specific error
> > +code being returned in a specific situation.)
> >  
> >  struct kvm_one_reg {
> >         __u64 id;
> > @@ -2258,10 +2260,12 @@ Architectures: all
> >  Type: vcpu ioctl
> >  Parameters: struct kvm_one_reg (in and out)
> >  Returns: 0 on success, negative value on failure
> > -Errors:
> > +Errors include:
> >    ENOENT:   no such register
> > -  EPERM:    register access forbidden for architecture-dependent reasons
> > -  EINVAL:   other errors, such as bad size encoding for a known register
> > +  EINVAL:   invalid register ID, or no such register
> > +  EPERM:    (arm64) register access not allowed before vcpu finalization
> > +(These error codes are indicative only: do not rely on a specific error
> > +code being returned in a specific situation.)
> >  
> >  This ioctl allows to receive the value of a single register implemented
> >  in a vcpu. The register to read is indicated by the "id" field of the
> > -- 
> > 2.1.4
> >
> 
> Reviewed-by: Andrew Jones <drjones@redhat.com>

Thanks
---Dave