linux-kernel - Re: [PATCH v3 0/6] Hyper-V: Implement hypervisor core collection

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Message-ID: <20251017225732.GC632885@liuwe-devbox-debian-v2.local>
Date: Fri, 17 Oct 2025 22:57:32 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Mukesh Rathor <mrathor@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, kys@...rosoft.com,
	haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	arnd@...db.de
Subject: Re: [PATCH v3 0/6] Hyper-V: Implement hypervisor core collection

On Fri, Oct 17, 2025 at 10:33:00PM +0000, Wei Liu wrote:
> On Mon, Oct 06, 2025 at 03:42:02PM -0700, Mukesh Rathor wrote:
> [...]
> > Mukesh Rathor (6):
> >   x86/hyperv: Rename guest crash shutdown function
> >   hyperv: Add two new hypercall numbers to guest ABI public header
> >   hyperv: Add definitions for hypervisor crash dump support
> >   x86/hyperv: Add trampoline asm code to transition from hypervisor
> >   x86/hyperv: Implement hypervisor RAM collection into vmcore
> >   x86/hyperv: Enable build of hypervisor crashdump collection files
> > 
> 
> Applied to hyperv-next. Thanks.

This breaks i386 build.

/work/linux-on-hyperv/linux.git/arch/x86/hyperv/hv_init.c: In function ‘hyperv_init’:
/work/linux-on-hyperv/linux.git/arch/x86/hyperv/hv_init.c:557:17: error: implicit declaration of function ‘hv_root_crash_init’ [-Werror=implicit-function-declaration]
  557 |                 hv_root_crash_init();
      |                 ^~~~~~~~~~~~~~~~~~

That's because CONFIG_MSHV_ROOT is only available on x86_64. And the
crash feature is guarded by CONFIG_MSHV_ROOT.

Applying the following diff fixes the build.

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index e28737ec7054..c1300339d2eb 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -554,7 +554,9 @@ void __init hyperv_init(void)
                memunmap(src);

                hv_remap_tsc_clocksource();
+#ifdef CONFIG_X86_64
                hv_root_crash_init();
+#endif
        } else {
                hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
                wrmsrq(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);

> 
> >  arch/x86/hyperv/Makefile        |   6 +
> >  arch/x86/hyperv/hv_crash.c      | 642 ++++++++++++++++++++++++++++++++
> >  arch/x86/hyperv/hv_init.c       |   1 +
> >  arch/x86/hyperv/hv_trampoline.S | 101 +++++
> >  arch/x86/include/asm/mshyperv.h |  13 +
> >  arch/x86/kernel/cpu/mshyperv.c  |   5 +-
> >  include/hyperv/hvgdk_mini.h     |   2 +
> >  include/hyperv/hvhdk_mini.h     |  55 +++
> >  8 files changed, 823 insertions(+), 2 deletions(-)
> >  create mode 100644 arch/x86/hyperv/hv_crash.c
> >  create mode 100644 arch/x86/hyperv/hv_trampoline.S
> > 
> > -- 
> > 2.36.1.vfs.0.0
> >