From: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> Sent: Monday, March 10, 2025 2:47 PM > > On 3/7/2025 9:38 AM, Michael Kelley wrote: > > From: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> > >>>> Reviewed-by: Wei Liu <wei.liu@xxxxxxxxxx> > >>>> Reviewed-by: Tianyu Lan <tiala@xxxxxxxxxxxxx> > >>>> --- > >>>> 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. > > > Thanks Michael - I don't think it would be an issue since the __weak version > would be defined in mshyperv.c itself, replacing the function pointer. Yes, sounds right to me. > > However, I went and tested this __weak version again with CONFIG_MSHV_ROOT=m > and it does not actually work. Everything seems ok at first (it compiles, > can insert the module), but upon starting a guest, the interrupts don't get > delivered to the root (or rather, they don't get handled by mshv_hander()). > > This seems to match with what the ld docs say - There's an option > LD_DYNAMIC_LINK to allow __weak symbols to be overridden by the dynamic > linker, but this is not enabled in the kernel. > Yeah, I recall learning the hard way that a symbol defined in a module doesn't override a __weak symbol in the kernel image. At the time, I gave up and took a different path, and didn't get as far as looking at 'ld' options like you did. :-) Michael
