RE: [PATCH v5 07/16] x86/hyperv: extract partition ID from Microsoft Hypervisor if necessary

[Michael Kelley <mikelley@microsoft.com>]

From: Wei Liu <wei.liu@kernel.org> Sent: Tuesday, February 2, 2021 7:04 AM
> 
> On Tue, Jan 26, 2021 at 12:48:37AM +0000, Michael Kelley wrote:
> > From: Wei Liu <wei.liu@kernel.org> Sent: Wednesday, January 20, 2021 4:01 AM
> > >
> > > We will need the partition ID for executing some hypercalls later.
> > >
> > > Signed-off-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> > > Co-Developed-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> > > Signed-off-by: Wei Liu <wei.liu@kernel.org>
> > > ---
> > > v3:
> > > 1. Make hv_get_partition_id static.
> > > 2. Change code structure a bit.
> > > ---
> > >  arch/x86/hyperv/hv_init.c         | 27 +++++++++++++++++++++++++++
> > >  arch/x86/include/asm/mshyperv.h   |  2 ++
> > >  include/asm-generic/hyperv-tlfs.h |  6 ++++++
> > >  3 files changed, 35 insertions(+)
> > >
> > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > > index 6f4cb40e53fe..fc9941bd8653 100644
> > > --- a/arch/x86/hyperv/hv_init.c
> > > +++ b/arch/x86/hyperv/hv_init.c
> > > @@ -26,6 +26,9 @@
> > >  #include <linux/syscore_ops.h>
> > >  #include <clocksource/hyperv_timer.h>
> > >
> > > +u64 hv_current_partition_id = ~0ull;
> > > +EXPORT_SYMBOL_GPL(hv_current_partition_id);
> > > +
> > >  void *hv_hypercall_pg;
> > >  EXPORT_SYMBOL_GPL(hv_hypercall_pg);
> > >
> > > @@ -331,6 +334,25 @@ static struct syscore_ops hv_syscore_ops = {
> > >  	.resume		= hv_resume,
> > >  };
> > >
> > > +static void __init hv_get_partition_id(void)
> > > +{
> > > +	struct hv_get_partition_id *output_page;
> > > +	u16 status;
> > > +	unsigned long flags;
> > > +
> > > +	local_irq_save(flags);
> > > +	output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
> > > +	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page) &
> > > +		HV_HYPERCALL_RESULT_MASK;
> > > +	if (status != HV_STATUS_SUCCESS) {
> >
> > Across the Hyper-V code in Linux, the way we check the hypercall result
> > is very inconsistent.  IMHO, the and'ing of hv_do_hypercall() with
> > HV_HYPERCALL_RESULT_MASK so that status can be a u16 is stylistically
> > a bit unusual.
> >
> > I'd like to see the hypercall result being stored into a u64 local variable.
> > Then the subsequent test for the status should 'and' the u64 with
> > HV_HYPERCALL_RESULT_MASK to determine the result code.
> > I've made a note to go fix the places that aren't doing it that way.
> >
> 
> I will fold in the following diff in the next version. I will also check
> if there are other instances in this patch series that need fixing.
> Pretty sure there are a few.
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index fc9941bd8653..6064f64a1295 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -337,14 +337,13 @@ static struct syscore_ops hv_syscore_ops = {
>  static void __init hv_get_partition_id(void)
>  {
>         struct hv_get_partition_id *output_page;
> -       u16 status;
> +       u64 status;
>         unsigned long flags;
> 
>         local_irq_save(flags);
>         output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
> -       status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page) &
> -               HV_HYPERCALL_RESULT_MASK;
> -       if (status != HV_STATUS_SUCCESS) {
> +       status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
> +       if ((status & HV_HYPERCALL_RESULT_MASK) != HV_STATUS_SUCCESS) {
>                 /* No point in proceeding if this failed */
>                 pr_err("Failed to get partition ID: %d\n", status);
>                 BUG();
> > > +		/* No point in proceeding if this failed */
> > > +		pr_err("Failed to get partition ID: %d\n", status);
> > > +		BUG();
> > > +	}
> > > +	hv_current_partition_id = output_page->partition_id;
> > > +	local_irq_restore(flags);
> > > +}
> > > +
> > >  /*
> > >   * This function is to be invoked early in the boot sequence after the
> > >   * hypervisor has been detected.
> > > @@ -426,6 +448,11 @@ void __init hyperv_init(void)
> > >
> > >  	register_syscore_ops(&hv_syscore_ops);
> > >
> > > +	if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
> > > +		hv_get_partition_id();
> >
> > Another place where the EBX value saved into the ms_hyperv structure
> > could be used.
> 
> If you're okay with my response earlier, this will be handled later in
> another patch (series).
> 

Yes, that's OK.  Andrea Parri's patch series for Isolated VMs is capturing the
EBX value as well.

Michael