linux-kernel - Re: [PATCH v3 5/6] x86/hyperv: Implement hypervisor RAM collection into vmcore

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Message-ID: <20260113111412.GAaWYpBFPPLRG-YxNt@fat_crate.local>
Date: Tue, 13 Jan 2026 12:14:12 +0100
From: Borislav Petkov <bp@...en8.de>
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, dave.hansen@...ux.intel.com,
	x86@...nel.org, hpa@...or.com, arnd@...db.de
Subject: Re: [PATCH v3 5/6] x86/hyperv: Implement hypervisor RAM collection
 into vmcore

On Mon, Oct 06, 2025 at 03:42:07PM -0700, Mukesh Rathor wrote:
> Introduce a new file to implement collection of hypervisor RAM into the
> vmcore collected by linux. By default, the hypervisor RAM is locked, ie,
> protected via hw page table. Hyper-V implements a disable hypercall which
> essentially devirtualizes the system on the fly. This mechanism makes the
> hypervisor RAM accessible to linux. Because the hypervisor RAM is already
> mapped into linux address space (as reserved RAM), it is automatically
> collected into the vmcore without extra work. More details of the
> implementation are available in the file prologue.
> 
> Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_crash.c | 642 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 642 insertions(+)
>  create mode 100644 arch/x86/hyperv/hv_crash.c

This breaks randconfig builds here:

arch/x86/hyperv/hv_crash.c:631:2: error: must use 'struct' tag to refer to type 'smp_ops'
  631 |         smp_ops.crash_stop_other_cpus = hv_crash_stop_other_cpus;
      |         ^
      |         struct 
arch/x86/hyperv/hv_crash.c:631:9: error: expected identifier or '('
  631 |         smp_ops.crash_stop_other_cpus = hv_crash_stop_other_cpus;
      |                ^
2 errors generated.
make[4]: *** [scripts/Makefile.build:287: arch/x86/hyperv/hv_crash.o] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [scripts/Makefile.build:544: arch/x86/hyperv] Error 2
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [scripts/Makefile.build:544: arch/x86] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/home/amd/kernel/linux/Makefile:2054: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2

config 01-18-21-randconfig-x86_64-13708.cfg attached. Note that this is
a clang build:

Ubuntu clang version 18.1.3 (1ubuntu1)

It fails with gcc too tho:

arch/x86/hyperv/hv_crash.c: In function ‘hv_root_crash_init’:
arch/x86/hyperv/hv_crash.c:631:9: error: ‘smp_ops’ undeclared (first use in this function)
  631 |         smp_ops.crash_stop_other_cpus = hv_crash_stop_other_cpus;
      |         ^~~~~~~
arch/x86/hyperv/hv_crash.c:631:9: note: each undeclared identifier is reported only once for each function it appears in
make[4]: *** [scripts/Makefile.build:287: arch/x86/hyperv/hv_crash.o] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [scripts/Makefile.build:544: arch/x86/hyperv] Error 2
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [scripts/Makefile.build:544: arch/x86] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/home/amd/kernel/linux/Makefile:2054: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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