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

Wei Liu
2021-02-02T15:06:32Z

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).

Wei.