linux-kernel - Re: [PATCH v2 07/17] x86/hyperv: extract partition ID from Microsoft Hypervisor if necessary

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Date:   Thu, 12 Nov 2020 16:44:39 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>
Cc:     virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Lillian Grassin-Drake <ligrassi@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v2 07/17] x86/hyperv: extract partition ID from
 Microsoft Hypervisor if necessary

Wei Liu <wei.liu@...nel.org> writes:

> We will need the partition ID for executing some hypercalls later.
>
> Signed-off-by: Lillian Grassin-Drake <ligrassi@...rosoft.com>
> Co-Developed-by: Sunil Muthuswamy <sunilmut@...rosoft.com>
> Signed-off-by: Wei Liu <wei.liu@...nel.org>
> ---
>  arch/x86/hyperv/hv_init.c         | 26 ++++++++++++++++++++++++++
>  arch/x86/include/asm/mshyperv.h   |  2 ++
>  include/asm-generic/hyperv-tlfs.h |  6 ++++++
>  3 files changed, 34 insertions(+)
>
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 7a2e37f025b0..73b0fb851f76 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -30,6 +30,9 @@
>  bool hv_root_partition;
>  EXPORT_SYMBOL_GPL(hv_root_partition);
>  
> +u64 hv_current_partition_id;
> +EXPORT_SYMBOL_GPL(hv_current_partition_id);
> +
>  void *hv_hypercall_pg;
>  EXPORT_SYMBOL_GPL(hv_hypercall_pg);
>  
> @@ -335,6 +338,26 @@ static struct syscore_ops hv_syscore_ops = {
>  	.resume		= hv_resume,
>  };
>  
> +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)
> +		pr_err("Failed to get partition ID: %d\n", status);
> +	else
> +		hv_current_partition_id = output_page->partition_id;

Nit: I'd suggest we simplify this to:

	if (status != HV_STATUS_SUCCESS) {
		pr_err("Failed to get partition ID: %d\n", status);
		BUG();
	}
	hv_current_partition_id = output_page->partition_id;

and drop BUG_ON() below;

> +	local_irq_restore(flags);
> +
> +	/* No point in proceeding if this failed */
> +	BUG_ON(status != HV_STATUS_SUCCESS);
> +}
> +
>  /*
>   * This function is to be invoked early in the boot sequence after the
>   * hypervisor has been detected.
> @@ -430,6 +453,9 @@ void __init hyperv_init(void)
>  
>  	register_syscore_ops(&hv_syscore_ops);
>  
> +	if (hv_root_partition)
> +		hv_get_partition_id();
> +


We don't seem to check that the partition has AccessPartitionId
privilege. While I guess that root partitions always have it, I'd
suggest we write this as:

	if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
		hv_get_partition_id();

	BUG_ON(hv_root_partition && !hv_current_partition_id);

for correctness. Also, we need to make sure '0' is not a valid partition
id and use e.g. -1 otherwise.

>  	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;

-- 
Vitaly