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

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Message-ID: <88b38aff-51b8-57d8-e548-00d42254a541@linux.microsoft.com>
Date: Tue, 13 Jan 2026 15:36:51 -0800
From: Mukesh R <mrathor@...ux.microsoft.com>
To: Borislav Petkov <bp@...en8.de>
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 1/13/26 03:14, Borislav Petkov wrote:
> 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
> 

Looks like needs some config option around it, probably SMP. Will take
a look in a day or two. Thanks for letting us know.

-Mukesh