[PATCH v2 0/2] hyperv: Move some features to common code

[PATCH v2 0/2] hyperv: Move some features to common code

[Nuno Das Neves]

There are several bits of Hyper-V-related code that today live in
arch/x86 but are not really specific to x86_64 and will work on arm64
too.

Some of these will be needed in the upcoming mshv driver code (for
Linux as root partition on Hyper-V). So this is a good time to move
them to drivers/hv.

Signed-off-by: Nuno Das Neves <nudasnev@microsoft.com>
---
Changes in v2:
* Fix dependence on percpu output page by using a stack variable for the
  hypercall output [Michael Kelley]
* Remove unnecessary WARN()s [Michael Kelley]
* Define hv_current_partition_id in hv_common.c [Michael Kelley]
* Move entire hv_proc.c to drivers/hv [Michael Kelley]

Nuno Das Neves (2):
  hyperv: Move hv_current_partition_id to arch-generic code
  hyperv: Move arch/x86/hyperv/hv_proc.c to drivers/hv

 arch/x86/hyperv/Makefile                  |  2 +-
 arch/x86/hyperv/hv_init.c                 | 26 -----------------------
 arch/x86/include/asm/mshyperv.h           |  6 ------
 drivers/hv/Makefile                       |  2 +-
 drivers/hv/hv_common.c                    | 23 ++++++++++++++++++++
 {arch/x86/hyperv => drivers/hv}/hv_proc.c |  4 ----
 include/asm-generic/mshyperv.h            |  5 +++++
 7 files changed, 30 insertions(+), 38 deletions(-)
 rename {arch/x86/hyperv => drivers/hv}/hv_proc.c (98%)

-- 
2.34.1

[PATCH v2 1/2] hyperv: Move hv_current_partition_id to arch-generic code

[Nuno Das Neves]

From: Nuno Das Neves <nudasnev@microsoft.com>

Move hv_current_partition_id and hv_get_partition_id() to hv_common.c.
These aren't specific to x86_64 and will be needed by common code.

Set hv_current_partition_id to HV_PARTITION_ID_SELF by default.

Use a stack variable for the output of the hypercall. This allows moving
the call of hv_get_partition_id() to hv_common_init() before the percpu
pages are initialized.

Remove the BUG()s. Failing to get the id need not crash the machine.

Signed-off-by: Nuno Das Neves <nudasnev@microsoft.com>
---
 arch/x86/hyperv/hv_init.c       | 26 --------------------------
 arch/x86/include/asm/mshyperv.h |  2 --
 drivers/hv/hv_common.c          | 23 +++++++++++++++++++++++
 include/asm-generic/mshyperv.h  |  1 +
 4 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 173005e6a95d..6b9f6f9f704d 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -34,9 +34,6 @@
 #include <clocksource/hyperv_timer.h>
 #include <linux/highmem.h>
 
-u64 hv_current_partition_id = ~0ull;
-EXPORT_SYMBOL_GPL(hv_current_partition_id);
-
 void *hv_hypercall_pg;
 EXPORT_SYMBOL_GPL(hv_hypercall_pg);
 
@@ -393,24 +390,6 @@ static void __init hv_stimer_setup_percpu_clockev(void)
 		old_setup_percpu_clockev();
 }
 
-static void __init hv_get_partition_id(void)
-{
-	struct hv_get_partition_id *output_page;
-	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);
-	if (!hv_result_success(status)) {
-		/* No point in proceeding if this failed */
-		pr_err("Failed to get partition ID: %lld\n", status);
-		BUG();
-	}
-	hv_current_partition_id = output_page->partition_id;
-	local_irq_restore(flags);
-}
-
 #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
 static u8 __init get_vtl(void)
 {
@@ -605,11 +584,6 @@ 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();
-
-	BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
-
 #ifdef CONFIG_PCI_MSI
 	/*
 	 * If we're running as root, we want to create our own PCI MSI domain.
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index f91ab1e75f9f..8d3ada3e8d0d 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -43,8 +43,6 @@ extern bool hyperv_paravisor_present;
 
 extern void *hv_hypercall_pg;
 
-extern u64 hv_current_partition_id;
-
 extern union hv_ghcb * __percpu *hv_ghcb_pg;
 
 bool hv_isolation_type_snp(void);
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index af5d1dc451f6..1da19b64ef16 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -31,6 +31,9 @@
 #include <hyperv/hvhdk.h>
 #include <asm/mshyperv.h>
 
+u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
+EXPORT_SYMBOL_GPL(hv_current_partition_id);
+
 /*
  * hv_root_partition, ms_hyperv and hv_nested are defined here with other
  * Hyper-V specific globals so they are shared across all architectures and are
@@ -283,6 +286,23 @@ static inline bool hv_output_page_exists(void)
 	return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
 }
 
+static void __init hv_get_partition_id(void)
+{
+	/*
+	 * Note in this case the output can be on the stack because it is just
+	 * a single u64 and hence won't cross a page boundary.
+	 */
+	struct hv_get_partition_id output;
+	u64 status;
+
+	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, &output);
+	if (!hv_result_success(status)) {
+		pr_err("Hyper-V: failed to get partition ID: %#lx\n", status);
+		return;
+	}
+	hv_current_partition_id = output.partition_id;
+}
+
 int __init hv_common_init(void)
 {
 	int i;
@@ -298,6 +318,9 @@ int __init hv_common_init(void)
 	if (hv_is_isolation_supported())
 		sysctl_record_panic_msg = 0;
 
+	if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
+		hv_get_partition_id();
+
 	/*
 	 * Hyper-V expects to get crash register data or kmsg when
 	 * crash enlightment is available and system crashes. Set
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index a7bbe504e4f3..98100466e0b2 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -58,6 +58,7 @@ struct ms_hyperv_info {
 };
 extern struct ms_hyperv_info ms_hyperv;
 extern bool hv_nested;
+extern u64 hv_current_partition_id;
 
 extern void * __percpu *hyperv_pcpu_input_arg;
 extern void * __percpu *hyperv_pcpu_output_arg;
-- 
2.34.1

RE: [PATCH v2 1/2] hyperv: Move hv_current_partition_id to arch-generic code

[Michael Kelley]

From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Wednesday, January 22, 2025 5:48 PM
> 
> Move hv_current_partition_id and hv_get_partition_id() to hv_common.c.
> These aren't specific to x86_64 and will be needed by common code.
> 
> Set hv_current_partition_id to HV_PARTITION_ID_SELF by default.
> 
> Use a stack variable for the output of the hypercall. This allows moving
> the call of hv_get_partition_id() to hv_common_init() before the percpu
> pages are initialized.
> 
> Remove the BUG()s. Failing to get the id need not crash the machine.
> 
> Signed-off-by: Nuno Das Neves <nudasnev@microsoft.com>
> ---
>  arch/x86/hyperv/hv_init.c       | 26 --------------------------
>  arch/x86/include/asm/mshyperv.h |  2 --
>  drivers/hv/hv_common.c          | 23 +++++++++++++++++++++++
>  include/asm-generic/mshyperv.h  |  1 +
>  4 files changed, 24 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 173005e6a95d..6b9f6f9f704d 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -34,9 +34,6 @@
>  #include <clocksource/hyperv_timer.h>
>  #include <linux/highmem.h>
> 
> -u64 hv_current_partition_id = ~0ull;
> -EXPORT_SYMBOL_GPL(hv_current_partition_id);
> -
>  void *hv_hypercall_pg;
>  EXPORT_SYMBOL_GPL(hv_hypercall_pg);
> 
> @@ -393,24 +390,6 @@ static void __init hv_stimer_setup_percpu_clockev(void)
>  		old_setup_percpu_clockev();
>  }
> 
> -static void __init hv_get_partition_id(void)
> -{
> -	struct hv_get_partition_id *output_page;
> -	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);
> -	if (!hv_result_success(status)) {
> -		/* No point in proceeding if this failed */
> -		pr_err("Failed to get partition ID: %lld\n", status);
> -		BUG();
> -	}
> -	hv_current_partition_id = output_page->partition_id;
> -	local_irq_restore(flags);
> -}
> -
>  #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
>  static u8 __init get_vtl(void)
>  {
> @@ -605,11 +584,6 @@ 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();
> -
> -	BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
> -
>  #ifdef CONFIG_PCI_MSI
>  	/*
>  	 * If we're running as root, we want to create our own PCI MSI domain.
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index f91ab1e75f9f..8d3ada3e8d0d 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -43,8 +43,6 @@ extern bool hyperv_paravisor_present;
> 
>  extern void *hv_hypercall_pg;
> 
> -extern u64 hv_current_partition_id;
> -
>  extern union hv_ghcb * __percpu *hv_ghcb_pg;
> 
>  bool hv_isolation_type_snp(void);
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index af5d1dc451f6..1da19b64ef16 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -31,6 +31,9 @@
>  #include <hyperv/hvhdk.h>
>  #include <asm/mshyperv.h>
> 
> +u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
> +EXPORT_SYMBOL_GPL(hv_current_partition_id);
> +
>  /*
>   * hv_root_partition, ms_hyperv and hv_nested are defined here with other
>   * Hyper-V specific globals so they are shared across all architectures and are
> @@ -283,6 +286,23 @@ static inline bool hv_output_page_exists(void)
>  	return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
>  }
> 
> +static void __init hv_get_partition_id(void)
> +{
> +	/*
> +	 * Note in this case the output can be on the stack because it is just
> +	 * a single u64 and hence won't cross a page boundary.
> +	 */
> +	struct hv_get_partition_id output;

It's unfortunate that the structure name "hv_get_partition_id" is also
the name of this function. Could the structure name be changed to
follow the pattern of having "output" in the name, like other hypercall
parameters? It's not a blocker if it can't be changed. I was just surprised
to search for "hv_get_partition_id" and find both uses.

Also, see the comment at the beginning of hv_query_ext_cap() regarding
using a local stack variable as hypercall input or output. The comment
originated here [1]. At that time, I didn't investigate Sunil's assertion any
further, and I'm still unsure whether it is really true. But perhaps for
consistency and safety we should follow what it says.

[1] https://lore.kernel.org/linux-hyperv/SN4PR2101MB0880DB0606A5A0B72AD244B4C06A9@SN4PR2101MB0880.namprd21.prod.outlook.com/

> +	u64 status;
> +
> +	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, &output);
> +	if (!hv_result_success(status)) {
> +		pr_err("Hyper-V: failed to get partition ID: %#lx\n", status);
> +		return;
> +	}
> +	hv_current_partition_id = output.partition_id;
> +}
> +
>  int __init hv_common_init(void)
>  {
>  	int i;
> @@ -298,6 +318,9 @@ int __init hv_common_init(void)
>  	if (hv_is_isolation_supported())
>  		sysctl_record_panic_msg = 0;
> 
> +	if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
> +		hv_get_partition_id();

I don't see how this works. On the x86 side, hv_common_init()
is called before the guest ID is set and the hypercall page is setup.
So the hypercall in hv_get_partition_id() should fail.

Michael

> +
>  	/*
>  	 * Hyper-V expects to get crash register data or kmsg when
>  	 * crash enlightment is available and system crashes. Set
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index a7bbe504e4f3..98100466e0b2 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -58,6 +58,7 @@ struct ms_hyperv_info {
>  };
>  extern struct ms_hyperv_info ms_hyperv;
>  extern bool hv_nested;
> +extern u64 hv_current_partition_id;
> 
>  extern void * __percpu *hyperv_pcpu_input_arg;
>  extern void * __percpu *hyperv_pcpu_output_arg;
> --
> 2.34.1

Re: [PATCH v2 1/2] hyperv: Move hv_current_partition_id to arch-generic code

[Nuno Das Neves]

On 1/28/2025 10:45 AM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Wednesday, January 22, 2025 5:48 PM
>>
>> Move hv_current_partition_id and hv_get_partition_id() to hv_common.c.
>> These aren't specific to x86_64 and will be needed by common code.
>>
>> Set hv_current_partition_id to HV_PARTITION_ID_SELF by default.
>>
>> Use a stack variable for the output of the hypercall. This allows moving
>> the call of hv_get_partition_id() to hv_common_init() before the percpu
>> pages are initialized.
>>
>> Remove the BUG()s. Failing to get the id need not crash the machine.
>>
>> Signed-off-by: Nuno Das Neves <nudasnev@microsoft.com>
>> ---
>>  arch/x86/hyperv/hv_init.c       | 26 --------------------------
>>  arch/x86/include/asm/mshyperv.h |  2 --
>>  drivers/hv/hv_common.c          | 23 +++++++++++++++++++++++
>>  include/asm-generic/mshyperv.h  |  1 +
>>  4 files changed, 24 insertions(+), 28 deletions(-)
>>
>> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
>> index 173005e6a95d..6b9f6f9f704d 100644
>> --- a/arch/x86/hyperv/hv_init.c
>> +++ b/arch/x86/hyperv/hv_init.c
>> @@ -34,9 +34,6 @@
>>  #include <clocksource/hyperv_timer.h>
>>  #include <linux/highmem.h>
>>
>> -u64 hv_current_partition_id = ~0ull;
>> -EXPORT_SYMBOL_GPL(hv_current_partition_id);
>> -
>>  void *hv_hypercall_pg;
>>  EXPORT_SYMBOL_GPL(hv_hypercall_pg);
>>
>> @@ -393,24 +390,6 @@ static void __init hv_stimer_setup_percpu_clockev(void)
>>  		old_setup_percpu_clockev();
>>  }
>>
>> -static void __init hv_get_partition_id(void)
>> -{
>> -	struct hv_get_partition_id *output_page;
>> -	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);
>> -	if (!hv_result_success(status)) {
>> -		/* No point in proceeding if this failed */
>> -		pr_err("Failed to get partition ID: %lld\n", status);
>> -		BUG();
>> -	}
>> -	hv_current_partition_id = output_page->partition_id;
>> -	local_irq_restore(flags);
>> -}
>> -
>>  #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
>>  static u8 __init get_vtl(void)
>>  {
>> @@ -605,11 +584,6 @@ 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();
>> -
>> -	BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
>> -
>>  #ifdef CONFIG_PCI_MSI
>>  	/*
>>  	 * If we're running as root, we want to create our own PCI MSI domain.
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index f91ab1e75f9f..8d3ada3e8d0d 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -43,8 +43,6 @@ extern bool hyperv_paravisor_present;
>>
>>  extern void *hv_hypercall_pg;
>>
>> -extern u64 hv_current_partition_id;
>> -
>>  extern union hv_ghcb * __percpu *hv_ghcb_pg;
>>
>>  bool hv_isolation_type_snp(void);
>> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
>> index af5d1dc451f6..1da19b64ef16 100644
>> --- a/drivers/hv/hv_common.c
>> +++ b/drivers/hv/hv_common.c
>> @@ -31,6 +31,9 @@
>>  #include <hyperv/hvhdk.h>
>>  #include <asm/mshyperv.h>
>>
>> +u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
>> +EXPORT_SYMBOL_GPL(hv_current_partition_id);
>> +
>>  /*
>>   * hv_root_partition, ms_hyperv and hv_nested are defined here with other
>>   * Hyper-V specific globals so they are shared across all architectures and are
>> @@ -283,6 +286,23 @@ static inline bool hv_output_page_exists(void)
>>  	return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
>>  }
>>
>> +static void __init hv_get_partition_id(void)
>> +{
>> +	/*
>> +	 * Note in this case the output can be on the stack because it is just
>> +	 * a single u64 and hence won't cross a page boundary.
>> +	 */
>> +	struct hv_get_partition_id output;
> 
> It's unfortunate that the structure name "hv_get_partition_id" is also
> the name of this function. Could the structure name be changed to
> follow the pattern of having "output" in the name, like other hypercall
> parameters? It's not a blocker if it can't be changed. I was just surprised
> to search for "hv_get_partition_id" and find both uses.
> 

hv_output_get_partition_id is really the "correct" name from the Hyper-V code,
so it makes sense to just change it to that in this patch.

> Also, see the comment at the beginning of hv_query_ext_cap() regarding
> using a local stack variable as hypercall input or output. The comment
> originated here [1]. At that time, I didn't investigate Sunil's assertion any
> further, and I'm still unsure whether it is really true. But perhaps for
> consistency and safety we should follow what it says.
> 
> [1] https://lore.kernel.org/linux-hyperv/SN4PR2101MB0880DB0606A5A0B72AD244B4C06A9@SN4PR2101MB0880.namprd21.prod.outlook.com/
> 
Hmm, from some cursory research it does look like stack variables can't be
used with virt_to_phys().

I thought about just using &hv_current_partition directly - I *think* that
will work - but in the end I think it's just simpler to just move calls so the
percpu output page can be used as normal. That may save some additional
back-and-forth as well as explanatory comments in the code.

I will also add a check for hv_output_page_exists() here, as a precaution in
case the HV_ACCESS_PARTITION_ID privilege ever becomes decoupled from
that (as it stands, I believe that permission is only for the root
partition, but you never know).

>> +	u64 status;
>> +
>> +	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, &output);
>> +	if (!hv_result_success(status)) {
>> +		pr_err("Hyper-V: failed to get partition ID: %#lx\n", status);
>> +		return;
>> +	}
>> +	hv_current_partition_id = output.partition_id;
>> +}
>> +
>>  int __init hv_common_init(void)
>>  {
>>  	int i;
>> @@ -298,6 +318,9 @@ int __init hv_common_init(void)
>>  	if (hv_is_isolation_supported())
>>  		sysctl_record_panic_msg = 0;
>>
>> +	if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
>> +		hv_get_partition_id();
> 
> I don't see how this works. On the x86 side, hv_common_init()
> is called before the guest ID is set and the hypercall page is setup.
> So the hypercall in hv_get_partition_id() should fail.
> 

Oh, I tried to get too clever. I will put it back where it was and
add it on the arm64 side to hyperv_init() after the per-cpu init as
I mentioned above.

Thanks for the comments,
Nuno

> Michael
> 
>> +
>>  	/*
>>  	 * Hyper-V expects to get crash register data or kmsg when
>>  	 * crash enlightment is available and system crashes. Set
>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index a7bbe504e4f3..98100466e0b2 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -58,6 +58,7 @@ struct ms_hyperv_info {
>>  };
>>  extern struct ms_hyperv_info ms_hyperv;
>>  extern bool hv_nested;
>> +extern u64 hv_current_partition_id;
>>
>>  extern void * __percpu *hyperv_pcpu_input_arg;
>>  extern void * __percpu *hyperv_pcpu_output_arg;
>> --
>> 2.34.1

RE: [PATCH v2 1/2] hyperv: Move hv_current_partition_id to arch-generic code

[Michael Kelley]

From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Tuesday, January 28, 2025 4:46 PM
> 
> On 1/28/2025 10:45 AM, Michael Kelley wrote:
> > From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Wednesday, January 22, 2025 5:48 PM
> >>
> >> Move hv_current_partition_id and hv_get_partition_id() to hv_common.c.
> >> These aren't specific to x86_64 and will be needed by common code.
> >>
> >> Set hv_current_partition_id to HV_PARTITION_ID_SELF by default.
> >>
> >> Use a stack variable for the output of the hypercall. This allows moving
> >> the call of hv_get_partition_id() to hv_common_init() before the percpu
> >> pages are initialized.
> >>
> >> Remove the BUG()s. Failing to get the id need not crash the machine.
> >>
> >> Signed-off-by: Nuno Das Neves <nudasnev@microsoft.com>
> >> ---
> >>  arch/x86/hyperv/hv_init.c       | 26 --------------------------
> >>  arch/x86/include/asm/mshyperv.h |  2 --
> >>  drivers/hv/hv_common.c          | 23 +++++++++++++++++++++++
> >>  include/asm-generic/mshyperv.h  |  1 +
> >>  4 files changed, 24 insertions(+), 28 deletions(-)

[snip]

> >> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> >> index af5d1dc451f6..1da19b64ef16 100644
> >> --- a/drivers/hv/hv_common.c
> >> +++ b/drivers/hv/hv_common.c
> >> @@ -31,6 +31,9 @@
> >>  #include <hyperv/hvhdk.h>
> >>  #include <asm/mshyperv.h>
> >>
> >> +u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
> >> +EXPORT_SYMBOL_GPL(hv_current_partition_id);
> >> +
> >>  /*
> >>   * hv_root_partition, ms_hyperv and hv_nested are defined here with other
> >>   * Hyper-V specific globals so they are shared across all architectures and are
> >> @@ -283,6 +286,23 @@ static inline bool hv_output_page_exists(void)
> >>  	return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
> >>  }
> >>
> >> +static void __init hv_get_partition_id(void)
> >> +{
> >> +	/*
> >> +	 * Note in this case the output can be on the stack because it is just
> >> +	 * a single u64 and hence won't cross a page boundary.
> >> +	 */
> >> +	struct hv_get_partition_id output;
> >
> > It's unfortunate that the structure name "hv_get_partition_id" is also
> > the name of this function. Could the structure name be changed to
> > follow the pattern of having "output" in the name, like other hypercall
> > parameters? It's not a blocker if it can't be changed. I was just surprised
> > to search for "hv_get_partition_id" and find both uses.
> >
> 
> hv_output_get_partition_id is really the "correct" name from the Hyper-V code,
> so it makes sense to just change it to that in this patch.
> 
> > Also, see the comment at the beginning of hv_query_ext_cap() regarding
> > using a local stack variable as hypercall input or output. The comment
> > originated here [1]. At that time, I didn't investigate Sunil's assertion any
> > further, and I'm still unsure whether it is really true. But perhaps for
> > consistency and safety we should follow what it says.
> >
> > [1] https://lore.kernel.org/linux-hyperv/SN4PR2101MB0880DB0606A5A0B72AD244B4C06A9@SN4PR2101MB0880.namprd21.prod.outlook.com/
> >
> Hmm, from some cursory research it does look like stack variables can't be
> used with virt_to_phys().
> 
> I thought about just using &hv_current_partition directly - I *think* that
> will work - but in the end I think it's just simpler to just move calls so the
> percpu output page can be used as normal. That may save some additional
> back-and-forth as well as explanatory comments in the code.
> 
> I will also add a check for hv_output_page_exists() here, as a precaution in
> case the HV_ACCESS_PARTITION_ID privilege ever becomes decoupled from
> that (as it stands, I believe that permission is only for the root
> partition, but you never know).

Or just use the hyperv_pcpu_input_page, even though the use here is
for output. Then you don't have to worry about whether the output
page exists.  FWIW, I'm working on a set of changes that encapsulates
the assignment of the per-cpu hypercall argument pages, and it does
away with the distinction between the input and output pages. But
that will come sometime after this patch.

Michael

> 
> >> +	u64 status;
> >> +
> >> +	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, &output);
> >> +	if (!hv_result_success(status)) {
> >> +		pr_err("Hyper-V: failed to get partition ID: %#lx\n", status);
> >> +		return;
> >> +	}
> >> +	hv_current_partition_id = output.partition_id;
> >> +}
> >> +
> >>  int __init hv_common_init(void)
> >>  {
> >>  	int i;
> >> @@ -298,6 +318,9 @@ int __init hv_common_init(void)
> >>  	if (hv_is_isolation_supported())
> >>  		sysctl_record_panic_msg = 0;
> >>
> >> +	if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
> >> +		hv_get_partition_id();
> >
> > I don't see how this works. On the x86 side, hv_common_init()
> > is called before the guest ID is set and the hypercall page is setup.
> > So the hypercall in hv_get_partition_id() should fail.
> >
> 
> Oh, I tried to get too clever. I will put it back where it was and
> add it on the arm64 side to hyperv_init() after the per-cpu init as
> I mentioned above.
> 
> Thanks for the comments,
> Nuno

[PATCH v2 2/2] hyperv: Move arch/x86/hyperv/hv_proc.c to drivers/hv

[Nuno Das Neves]

These helpers are not specific to x86_64 and will be needed by common code.
Remove some unnecessary #includes.

Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
---
 arch/x86/hyperv/Makefile                  | 2 +-
 arch/x86/include/asm/mshyperv.h           | 4 ----
 drivers/hv/Makefile                       | 2 +-
 {arch/x86/hyperv => drivers/hv}/hv_proc.c | 4 ----
 include/asm-generic/mshyperv.h            | 4 ++++
 5 files changed, 6 insertions(+), 10 deletions(-)
 rename {arch/x86/hyperv => drivers/hv}/hv_proc.c (98%)

diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
index 3a1548054b48..d55f494f471d 100644
--- a/arch/x86/hyperv/Makefile
+++ b/arch/x86/hyperv/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y			:= hv_init.o mmu.o nested.o irqdomain.o ivm.o
-obj-$(CONFIG_X86_64)	+= hv_apic.o hv_proc.o
+obj-$(CONFIG_X86_64)	+= hv_apic.o
 obj-$(CONFIG_HYPERV_VTL_MODE)	+= hv_vtl.o
 
 ifdef CONFIG_X86_64
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 8d3ada3e8d0d..7dfca93ef048 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -56,10 +56,6 @@ u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
 #define HV_AP_INIT_GPAT_DEFAULT		0x0007040600070406ULL
 #define HV_AP_SEGMENT_LIMIT		0xffffffff
 
-int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
-int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
-int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
-
 /*
  * If the hypercall involves no input or output parameters, the hypervisor
  * ignores the corresponding GPA pointer.
diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
index b992c0ed182b..9afcabb3fbd2 100644
--- a/drivers/hv/Makefile
+++ b/drivers/hv/Makefile
@@ -13,4 +13,4 @@ hv_vmbus-$(CONFIG_HYPERV_TESTING)	+= hv_debugfs.o
 hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
 
 # Code that must be built-in
-obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o
+obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o hv_proc.o
diff --git a/arch/x86/hyperv/hv_proc.c b/drivers/hv/hv_proc.c
similarity index 98%
rename from arch/x86/hyperv/hv_proc.c
rename to drivers/hv/hv_proc.c
index ac4c834d4435..3e410489f480 100644
--- a/arch/x86/hyperv/hv_proc.c
+++ b/drivers/hv/hv_proc.c
@@ -6,11 +6,7 @@
 #include <linux/slab.h>
 #include <linux/cpuhotplug.h>
 #include <linux/minmax.h>
-#include <asm/hypervisor.h>
 #include <asm/mshyperv.h>
-#include <asm/apic.h>
-
-#include <asm/trace/hyperv.h>
 
 /*
  * See struct hv_deposit_memory. The first u64 is partition ID, the rest
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index 98100466e0b2..faf5d27a76b1 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -217,6 +217,10 @@ void *hv_alloc_hyperv_page(void);
 void *hv_alloc_hyperv_zeroed_page(void);
 void hv_free_hyperv_page(void *addr);
 
+int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
+int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
+int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
+
 /**
  * hv_cpu_number_to_vp_number() - Map CPU to VP.
  * @cpu_number: CPU number in Linux terms
-- 
2.34.1

RE: [PATCH v2 2/2] hyperv: Move arch/x86/hyperv/hv_proc.c to drivers/hv

[Michael Kelley]

From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Wednesday, January 22, 2025 5:48 PM
> 
> These helpers are not specific to x86_64 and will be needed by common code.
> Remove some unnecessary #includes.
> 
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> ---
>  arch/x86/hyperv/Makefile                  | 2 +-
>  arch/x86/include/asm/mshyperv.h           | 4 ----
>  drivers/hv/Makefile                       | 2 +-
>  {arch/x86/hyperv => drivers/hv}/hv_proc.c | 4 ----
>  include/asm-generic/mshyperv.h            | 4 ++++
>  5 files changed, 6 insertions(+), 10 deletions(-)
>  rename {arch/x86/hyperv => drivers/hv}/hv_proc.c (98%)
> 
> diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
> index 3a1548054b48..d55f494f471d 100644
> --- a/arch/x86/hyperv/Makefile
> +++ b/arch/x86/hyperv/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  obj-y			:= hv_init.o mmu.o nested.o irqdomain.o ivm.o
> -obj-$(CONFIG_X86_64)	+= hv_apic.o hv_proc.o
> +obj-$(CONFIG_X86_64)	+= hv_apic.o
>  obj-$(CONFIG_HYPERV_VTL_MODE)	+= hv_vtl.o
> 
>  ifdef CONFIG_X86_64
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 8d3ada3e8d0d..7dfca93ef048 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -56,10 +56,6 @@ u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
>  #define HV_AP_INIT_GPAT_DEFAULT		0x0007040600070406ULL
>  #define HV_AP_SEGMENT_LIMIT		0xffffffff
> 
> -int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
> -int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
> -int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
> -
>  /*
>   * If the hypercall involves no input or output parameters, the hypervisor
>   * ignores the corresponding GPA pointer.
> diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
> index b992c0ed182b..9afcabb3fbd2 100644
> --- a/drivers/hv/Makefile
> +++ b/drivers/hv/Makefile
> @@ -13,4 +13,4 @@ hv_vmbus-$(CONFIG_HYPERV_TESTING)	+= hv_debugfs.o
>  hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
> 
>  # Code that must be built-in
> -obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o
> +obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o hv_proc.o
> diff --git a/arch/x86/hyperv/hv_proc.c b/drivers/hv/hv_proc.c
> similarity index 98%
> rename from arch/x86/hyperv/hv_proc.c
> rename to drivers/hv/hv_proc.c
> index ac4c834d4435..3e410489f480 100644
> --- a/arch/x86/hyperv/hv_proc.c
> +++ b/drivers/hv/hv_proc.c
> @@ -6,11 +6,7 @@
>  #include <linux/slab.h>
>  #include <linux/cpuhotplug.h>
>  #include <linux/minmax.h>
> -#include <asm/hypervisor.h>
>  #include <asm/mshyperv.h>
> -#include <asm/apic.h>
> -
> -#include <asm/trace/hyperv.h>
> 
>  /*
>   * See struct hv_deposit_memory. The first u64 is partition ID, the rest
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 98100466e0b2..faf5d27a76b1 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -217,6 +217,10 @@ void *hv_alloc_hyperv_page(void);
>  void *hv_alloc_hyperv_zeroed_page(void);
>  void hv_free_hyperv_page(void *addr);
> 
> +int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
> +int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
> +int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
> +
>  /**
>   * hv_cpu_number_to_vp_number() - Map CPU to VP.
>   * @cpu_number: CPU number in Linux terms
> --
> 2.34.1

Reviewed-by: Michael Kelley <mhklinux@outlook.com>