linux-kernel - Re: [PATCH v9 10/27] gunyah: rsc

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Message-ID: <4a584563-1fb7-22fa-5e16-e0cf5e88b76b@linaro.org>
Date:   Mon, 6 Feb 2023 09:41:11 -0600
From:   Alex Elder <elder@...aro.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Elliot Berman <quic_eberman@...cinc.com>,
        Bjorn Andersson <quic_bjorande@...cinc.com>,
        Murali Nalajala <quic_mnalajal@...cinc.com>
Cc:     Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Sudeep Holla <sudeep.holla@....com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 10/27] gunyah: rsc_mgr: Add VM lifecycle RPC

On 2/2/23 6:46 AM, Srinivas Kandagatla wrote:
>> +    ret = gh_rm_call(rm, message_id, &req_payload, 
>> sizeof(req_payload), &resp, &resp_size);
>> +    if (!ret && resp_size) {
> 
> Am struggling to understand these type of checks in success case, when a 
> command is not expecting any response why are we checking for response 
> here, This sounds like a bug in either RM or hypervisor.
> 
> Or Is this something that happens due to some firmware behaviour?
> Could you elobrate on this.

What I think you're talking about is error checking even when
it's very clear something "can't happen."  It's a pattern I've
seen in Qualcomm downstream code, and I believe sometimes it
is done as "best practice" to avoid warnings from security scans.
(I might be wrong about this though.)

I think your underlying point though is that we can just assume
success means "truly successful," so there's no reason to do any
additional sanity checks.  We *assume* the hardware is doing the
correct thing (if it's not, we might as well assume it does
*nothing* right).

So as a very general statement, I think all checks of this type
should go away (and I think Srini would agree).

					-Alex