Re: [PATCH v8 06/28] virt: gunyah: Identify hypervisor version

[Alex Elder]

On 1/10/23 11:56 AM, Elliot Berman wrote:
> 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@xxxxxxxxxxx>
> > > ---
> > >   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,
> };

My point wasn't necessarily to expose all of that.  Already
"gunyah.h" defines the bit positions in which these things
are recorded in the identify response.  My main point was
about (not) exposing that global variable.

I support your suggestion of abstracting the feature
interface that way, but I suggest waiting until it's
actually needed before you add it.  I don't see any
code that uses GH_IDENTIFY_PARTITION_CSPACE (and the
rest) currently.

Oh, and interestingly enough I see GH_API_INFO_BIG_ENDIAN
defined in the API info...

					-Alex

> u16 gh_api_version(void);
> bool gh_api_has_feature(enum gh_api_feature feature);
>
> Thanks,
> Elliot