Re: [PATCH v5 08/10] x86: hyperv: Add mshv_handler irq handler and setup function

Nuno Das Neves
2025-03-07T23:29:59Z

On 3/7/2025 9:44 AM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Wednesday, February 26, 2025 3:08 PM
>
>>
>> This will handle SYNIC interrupts such as intercepts, doorbells, and
>> scheduling messages intended for the mshv driver.
>
> Could you provide a bit more detailed commit message? How does
> the mshv_handler() relate to the vmbus_handler()? From the code
> mshv_handler() goes first, and I'm assuming it processes what it
> knows about (intercepts, doorbells, scheduling messages?) and
> then hands off control to the vmbus_handler() to handle the usual
> VMbus-related message and channel interrupts. But it would be
> nice to have the commit message or code comments describe the
> overall intent and any obscure aspects of the relationship.
>
> And avoid references to "This" or "This patch". :-)
>

You've described it pretty well, I don't know if there's too much
more to say given this patch doesn't introduce the handler code.

I can try to improve it, something like:
"
mshv_handler() will be used to process messages related to managing
guest partitions such as intercepts, doorbells, and scheduling messages.

In a (non-nested) root partition, the same interrupt vector is shared
between the vmbus and mshv_root drivers.

Introduce a stub for mshv_handler() and call it in
sysvec_hyperv_callback alongside vmbus_handler().

Even though both handlers will be called for every Hyper-V interrupt,
the messages for each driver are delivered to different offsets within
the SYNIC message page, so they won't step on each other.
"

Does that work?

Nuno
>>
>> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
>> Reviewed-by: Wei Liu <wei.liu@kernel.org>
>> Reviewed-by: Tianyu Lan <tiala@microsoft.com>
>> ---
>> arch/x86/kernel/cpu/mshyperv.c | 9 +++++++++
>> drivers/hv/hv_common.c | 5 +++++
>> include/asm-generic/mshyperv.h | 1 +
>> 3 files changed, 15 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
>> index 0116d0e96ef9..616e9a5d77b4 100644
>> --- a/arch/x86/kernel/cpu/mshyperv.c
>> +++ b/arch/x86/kernel/cpu/mshyperv.c
>> @@ -107,6 +107,7 @@ void hv_set_msr(unsigned int reg, u64 value)
>> }
>> EXPORT_SYMBOL_GPL(hv_set_msr);
>>
>> +static void (*mshv_handler)(void);
>> static void (*vmbus_handler)(void);
>> static void (*hv_stimer0_handler)(void);
>> static void (*hv_kexec_handler)(void);
>> @@ -117,6 +118,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
>> struct pt_regs *old_regs = set_irq_regs(regs);
>>
>> inc_irq_stat(irq_hv_callback_count);
>> + if (mshv_handler)
>> + mshv_handler();
>> +
>> if (vmbus_handler)
>> vmbus_handler();
>>
>> @@ -126,6 +130,11 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
>> set_irq_regs(old_regs);
>> }
>>
>> +void hv_setup_mshv_handler(void (*handler)(void))
>> +{
>> + mshv_handler = handler;
>> +}
>> +
>> void hv_setup_vmbus_handler(void (*handler)(void))
>> {
>> vmbus_handler = handler;
>> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
>> index 2763cb6d3678..f5a07fd9a03b 100644
>> --- a/drivers/hv/hv_common.c
>> +++ b/drivers/hv/hv_common.c
>> @@ -677,6 +677,11 @@ void __weak hv_remove_vmbus_handler(void)
>> }
>> EXPORT_SYMBOL_GPL(hv_remove_vmbus_handler);
>>
>> +void __weak hv_setup_mshv_handler(void (*handler)(void))
>> +{
>> +}
>> +EXPORT_SYMBOL_GPL(hv_setup_mshv_handler);
>> +
>> void __weak hv_setup_kexec_handler(void (*handler)(void))
>> {
>> }
>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index 1f46d19a16aa..a05f12e63ccd 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -208,6 +208,7 @@ void hv_setup_kexec_handler(void (*handler)(void));
>> void hv_remove_kexec_handler(void);
>> void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs));
>> void hv_remove_crash_handler(void);
>> +void hv_setup_mshv_handler(void (*handler)(void));
>>
>> extern int vmbus_interrupt;
>> extern int vmbus_irq;
>> --
>> 2.34.1