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

Michael Kelley
2025-03-07T17:38:32Z

From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Friday, February 28, 2025 4:38 PM
>
> On 2/26/2025 3:43 PM, Stanislav Kinsburskii wrote:
> > On Wed, Feb 26, 2025 at 03:08:02PM -0800, Nuno Das Neves wrote:
> >> This will handle SYNIC interrupts such as intercepts, doorbells, and
> >> scheduling messages intended for the mshv driver.
> >>
> >> 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();
> >
> > Can mshv_handler be defined as a weak symbol doing nothing instead
> > of defining it a null pointer?
> > This should allow to simplify this code and get rid of
> > hv_setup_mshv_handler, which looks redundant.
> >
> Interesting, I tested this and it does seems to work! It seems like
> a good change, thanks.

Just be a bit careful. When CONFIG_HYPERV=n, mshyperv.c still gets
built even through none of the other Hyper-V related files do. There
are #ifdef CONFIG_HYPERV in mshyperv.c to eliminate references to
Hyper-V files that wouldn't be built. I'd suggest doing a test build with
that configuration to make sure it's all clean.

Michael

>
> > Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> >
> >> +
> >> 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
> >>