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

From: Michael Kelley <mikelley@microsoft.com>
To: Wei Liu <wei.liu@kernel.org>,
	Linux on Hyper-V List <linux-hyperv@vger.kernel.org>
Cc: "virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	Linux Kernel List <linux-kernel@vger.kernel.org>,
	Vineeth Pillai <viremana@linux.microsoft.com>,
	Sunil Muthuswamy <sunilmut@microsoft.com>,
	Nuno Das Neves <nunodasneves@linux.microsoft.com>,
	"pasha.tatashin@soleen.com" <pasha.tatashin@soleen.com>,
	Lillian Grassin-Drake <Lillian.GrassinDrake@microsoft.com>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Arnd Bergmann <arnd@arndb.de>,
	"open list:GENERIC INCLUDE/ASM HEADER FILES" 
	<linux-arch@vger.kernel.org>
Subject: RE: [PATCH v5 07/16] x86/hyperv: extract partition ID from Microsoft Hypervisor if necessary
Date: Tue, 26 Jan 2021 00:48:37 +0000	[thread overview]
Message-ID: <MWHPR21MB15932CD9CB9DA046EFFBA310D7BC9@MWHPR21MB1593.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20210120120058.29138-8-wei.liu@kernel.org>

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