linux-kernel - Re: [PATCH v8 05/28] virt: gunyah: Add hypercalls to identify Gunyah

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Message-ID: <b2819f68-8672-4909-c787-d1bdbd35da2e@linaro.org>
Date:   Tue, 17 Jan 2023 13:20:58 -0600
From:   Alex Elder <elder@...aro.org>
To:     Elliot Berman <quic_eberman@...cinc.com>,
        Alex Elder <elder@...aro.org>,
        Bjorn Andersson <quic_bjorande@...cinc.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        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>,
        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>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        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, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v8 05/28] virt: gunyah: Add hypercalls to identify Gunyah

On 1/10/23 11:56 AM, Elliot Berman wrote:
>>> There are two calls to help identify Gunyah:
>>>
>>> 1. gh_hypercall_get_uid() returns a UID when running under a Gunyah
>>>     hypervisor.
>>> 2. gh_hypercall_hyp_identify() returns build information and a set of
>>>     feature flags that are supported by Gunyah.
>>
>> The first is a "service", while the second is a "hypercall".
>> Can you explain the distinction?  The sentence at the top
>> refers to both as "hypercalls".
>>
> 
> I learned more details about this to answer your question. "get_uid()" 
> is a standardized call that is ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID 
> defined in include/arm-smccc.h. I'll use that.

You didn't really explain the distinction between hypercall
and service in Gunyah.  Both are encoded as "vendor specific
hypervisor service calls" according to the SVCCC specification.
I haven't found where ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID
gets handled, but I accept your answer that it's basically
a standard call.  The "get UID" is the only one that's defined
as a Gunyah "service"; the rest are hypercalls.

It's not a big deal, I just noticed the difference and was
curious about it.

					-Alex