linux-kernel - Re: [PATCH v17 15/35] virt: gunyah: Add proxy-scheduled vCPUs

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Date: Wed, 24 Apr 2024 10:01:10 -0700
From: Elliot Berman <quic_eberman@...cinc.com>
To: Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>
CC: Alex Elder <elder@...aro.org>,
        Srinivas Kandagatla
	<srinivas.kandagatla@...aro.org>,
        Murali Nalajal <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Carl van Schaik
	<quic_cvanscha@...cinc.com>,
        Philip Derrin <quic_pderrin@...cinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Jonathan Corbet
	<corbet@....net>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        "Fuad
 Tabba" <tabba@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Andrew
 Morton" <akpm@...ux-foundation.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v17 15/35] virt: gunyah: Add proxy-scheduled vCPUs

On Wed, Apr 24, 2024 at 03:09:57PM +0530, Srivatsa Vaddagiri wrote:
> * Elliot Berman <quic_eberman@...cinc.com> [2024-02-22 15:16:38]:
> 
> > +/**
> > + * struct gunyah_vm_exit_info - Reason for VM exit as reported by Gunyah
> > + * See Gunyah documentation for values.
> > + * @type: Describes how VM exited
> > + * @padding: padding bytes
> > + * @reason_size: Number of bytes valid for `reason`
> > + * @reason: See Gunyah documentation for interpretation. Note: these values are
> > + *          not interpreted by Linux and need to be converted from little-endian
> > + *          as applicable.
> > + */
> > +struct gunyah_vm_exit_info {
> > +	__u16 type;
> 
> Pls add an enum to describe the various exit types.
> 

When I was first added the exit_info, I thought a bunch on whether to
add the enum. I was thinking that if we add it to the UAPI, kernel need
to parse and validate the values from RM. In the current scheme, I can
leave it to userspace to interpret the value from RM. I could be
convinced to go the other way though. Currently this is less code :) Let
me know your thoughts! 

> > +	__u16 padding;
> > +	__u32 reason_size;
> > +	__u8 reason[GUNYAH_VM_MAX_EXIT_REASON_SIZE];

If we start interpreting the @type, then maybe we should also start
interpreting the @reason, and that will also add debt to the kernel
driver.

Thanks,
Elliot