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Date:   Tue, 10 Jan 2023 09:56:40 -0800
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From:   Elliot Berman <quic_eberman@quicinc.com>
Subject: Re: [PATCH v8 06/28] virt: gunyah: Identify hypervisor version
To:     Alex Elder <elder@linaro.org>,
        Bjorn Andersson <quic_bjorande@quicinc.com>,
        Murali Nalajala <quic_mnalajal@quicinc.com>
CC:     Trilok Soni <quic_tsoni@quicinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@quicinc.com>,
        Carl van Schaik <quic_cvanscha@quicinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "Bagas Sanjaya" <bagasdotme@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Jassi Brar <jassisinghbrar@gmail.com>,
        "Sudeep Holla" <sudeep.holla@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Lorenzo Pieralisi" <lpieralisi@kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        <linux-arm-msm@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-acpi@vger.kernel.org>
References: <20221219225850.2397345-1-quic_eberman@quicinc.com>
 <20221219225850.2397345-7-quic_eberman@quicinc.com>
 <51c36831-19c1-dd67-9e31-87733c190a9c@linaro.org>
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On 1/9/2023 1:34 PM, Alex Elder wrote:
> On 12/19/22 4:58 PM, Elliot Berman wrote:
>> Export the version of Gunyah which is reported via the hyp_identify
>> hypercall. Increments of the major API version indicate possibly
>> backwards incompatible changes.
>>
>> Export the hypervisor identity so that Gunyah drivers can act according
>> to the major API version.
>>
>> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
>> ---
>>   drivers/virt/Makefile        |  1 +
>>   drivers/virt/gunyah/Makefile |  1 +
>>   drivers/virt/gunyah/gunyah.c | 46 ++++++++++++++++++++++++++++++++++++
>>   include/linux/gunyah.h       |  6 +++++
>>   4 files changed, 54 insertions(+)
>>   create mode 100644 drivers/virt/gunyah/Makefile
>>   create mode 100644 drivers/virt/gunyah/gunyah.c
>>
>> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
>> index 093674e05c40..92b7e5311548 100644
>> --- a/drivers/virt/Makefile
>> +++ b/drivers/virt/Makefile
>> @@ -11,3 +11,4 @@ obj-$(CONFIG_NITRO_ENCLAVES)    += nitro_enclaves/
>>   obj-$(CONFIG_ACRN_HSM)        += acrn/
>>   obj-$(CONFIG_EFI_SECRET)    += coco/efi_secret/
>>   obj-$(CONFIG_SEV_GUEST)       += coco/sev-guest/
>> +obj-y                += gunyah/
>> diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
>> new file mode 100644
>> index 000000000000..2ac4ee64b89d
>> --- /dev/null
>> +++ b/drivers/virt/gunyah/Makefile
>> @@ -0,0 +1 @@
>> +obj-$(CONFIG_GUNYAH) += gunyah.o
>> diff --git a/drivers/virt/gunyah/gunyah.c b/drivers/virt/gunyah/gunyah.c
>> new file mode 100644
>> index 000000000000..c34c9046fc08
>> --- /dev/null
>> +++ b/drivers/virt/gunyah/gunyah.c
>> @@ -0,0 +1,46 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (c) 2022 Qualcomm Innovation Center, Inc. All rights 
>> reserved.
>> + */
>> +
>> +#define pr_fmt(fmt) "gunyah: " fmt
>> +
>> +#include <linux/gunyah.h>
>> +#include <linux/init.h>
>> +#include <linux/module.h>
>> +#include <linux/printk.h>
>> +
>> +struct gh_hypercall_hyp_identify_resp gunyah_api;
>> +EXPORT_SYMBOL_GPL(gunyah_api);
>> +
>> +static const uint32_t gunyah_known_uuids[][4] = {
>> +    {0x19bd54bd, 0x0b37571b, 0x946f609b, 0x54539de6}, /*QC_HYP 
>> (Qualcomm's build) */
>> +    {0x673d5f14, 0x9265ce36, 0xa4535fdb, 0xc1d58fcd}, /*GUNYAH (open 
>> source build) */
>> +};
>> +
>> +static int __init gunyah_init(void)
>> +{
>> +    u32 uid[4];
>> +    int i;
>> +
>> +    gh_hypercall_get_uid(uid);
>> +
>> +    for (i = 0; i < ARRAY_SIZE(gunyah_known_uuids); i++)
>> +        if (!memcmp(uid, gunyah_known_uuids[i], sizeof(uid)))
>> +            break;
>> +
>> +    if (i == ARRAY_SIZE(gunyah_known_uuids))
>> +        return -ENODEV;
>> +
>> +    gh_hypercall_hyp_identify(&gunyah_api);
>> +
>> +    pr_info("Running under Gunyah hypervisor %llx/v%u\n",
>> +        FIELD_GET(GH_API_INFO_VARIANT_MASK, gunyah_api.api_info),
>> +        gh_api_version());
>> +
>> +    return 0;
>> +}
>> +arch_initcall(gunyah_init);
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_DESCRIPTION("Gunyah Hypervisor Driver");
>> diff --git a/include/linux/gunyah.h b/include/linux/gunyah.h
>> index 2765d2b40198..166156f69df9 100644
>> --- a/include/linux/gunyah.h
>> +++ b/include/linux/gunyah.h
>> @@ -92,6 +92,12 @@ struct gh_hypercall_hyp_identify_resp {
>>       u64 api_info;
>>       u64 flags[3];
>>   };
>> +extern struct gh_hypercall_hyp_identify_resp gunyah_api;
> 
> Must this global variable be exposed?  Can't you hide it--as
> well as its interpretation--inside "gunyah.c"?
>  >> +
>> +static inline u16 gh_api_version(void)
>> +{
>> +    return FIELD_GET(GH_API_INFO_API_VERSION_MASK, gunyah_api.api_info);
>> +}
> 
> If you don't make the above function inline, can you hide the
> definition of gunyah_api?
> 

This seems like a good idea to me. I'm thinking to have the following 
functions:

enum gh_api_feature {
	GH_API_FEATURE_DOORBELL,
	GH_API_FEATURE_MSGQUEUE,
	GH_API_FEATURE_VIC,
	GH_API_FEATURE_VPM,
	GH_API_FEATURE_VCPU,
	GH_API_FEATURE_MEMEXTENT,
	GH_API_FEATURE_TRACE_CTRL,
};

u16 gh_api_version(void);
bool gh_api_has_feature(enum gh_api_feature feature);

Thanks,
Elliot