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

Michael Kelley
2021-01-26T10:39:17Z

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.

> + /* 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.

> +
> + BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
> +
> return;
>
> remove_cpuhp_state:
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 62d9390f1ddf..67f5d35a73d3 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -78,6 +78,8 @@ extern void *hv_hypercall_pg;
> extern void __percpu **hyperv_pcpu_input_arg;
> extern void __percpu **hyperv_pcpu_output_arg;
>
> +extern u64 hv_current_partition_id;
> +
> static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
> {
> u64 input_address = input ? virt_to_phys(input) : 0;
> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index e6903589a82a..87b1a79b19eb 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -141,6 +141,7 @@ struct ms_hyperv_tsc_page {
> #define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX 0x0013
> #define HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX 0x0014
> #define HVCALL_SEND_IPI_EX 0x0015
> +#define HVCALL_GET_PARTITION_ID 0x0046
> #define HVCALL_GET_VP_REGISTERS 0x0050
> #define HVCALL_SET_VP_REGISTERS 0x0051
> #define HVCALL_POST_MESSAGE 0x005c
> @@ -407,6 +408,11 @@ struct hv_tlb_flush_ex {
> u64 gva_list[];
> } __packed;
>
> +/* HvGetPartitionId hypercall (output only) */
> +struct hv_get_partition_id {
> + u64 partition_id;
> +} __packed;
> +
> /* HvRetargetDeviceInterrupt hypercall */
> union hv_msi_entry {
> u64 as_uint64;
> --
> 2.20.1