linux-kernel - Re: [PATCH v6 04/18] KVM: arm64: Support SDEI_EVENT

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Message-ID: <Ym9TarUE6+lJ0izt@google.com>
Date:   Mon, 2 May 2022 03:43:38 +0000
From:   Oliver Upton <oupton@...gle.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        eauger@...hat.com, Jonathan.Cameron@...wei.com,
        vkuznets@...hat.com, will@...nel.org, shannon.zhaosl@...il.com,
        james.morse@....com, mark.rutland@....com, maz@...nel.org,
        pbonzini@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v6 04/18] KVM: arm64: Support SDEI_EVENT_REGISTER
 hypercall

On Mon, May 02, 2022 at 10:55:51AM +0800, Gavin Shan wrote:
> > > +	unsigned long route_mode = smccc_get_arg(vcpu, 4);
> > 
> > This is really 'flags'. route_mode is bit[0]. I imagine we don't want to
> > support relative mode, so bit[1] is useless for us in that case too.
> > 
> > The spec is somewhat imprecise on what happens for reserved flags. The
> > prototype in section 5.1.2 of [1] suggests that reserved bits must be
> > zero, but 5.1.2.3 'Client responsibilities' does not state that invalid
> > flags result in an error.
> > 
> > Arm TF certainly rejects unexpected flags [2].
> > 
> > [1]: DEN0054C https://developer.arm.com/documentation/den0054/latest
> > [2]: https://github.com/ARM-software/arm-trusted-firmware/blob/66c3906e4c32d675eb06bd081de8a3359f76b84c/services/std_svc/sdei/sdei_main.c#L260
> > 
> 
> Yes, This chunk of code is still stick to old specification. Lets
> improve in next respin:
> 
>    - Rename @route_mode to @flags
>    - Reject if the reserved bits are set.
>    - Reject if relative mode (bit#1) is selected.
>    - Reject if routing mode (bit#0) isn't RM_ANY (0).

Bit[0] is ignored for private events, actually. So we really just reject
if any of bit[63:1] are set.

--
Thanks,
Oliver