NetBSD Problem Report #59715

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Date: Mon, 20 Oct 2025 00:02:49 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: nvmm: missing some MTRR MSRs
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>Number:         59715
>Category:       kern
>Synopsis:       nvmm: missing some MTRR MSRs
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Oct 20 00:05:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current, 11, 10, 9, ...
>Organization:
An Unexpected MSRty
>Environment:
>Description:
NetBSD probes some MSRs that NVMM doesn't recognize, leading to annoying and rather useless messages on the console:

qemu-system-i386: NVMM: Unexpected RDMSR 0x250, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x258, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x259, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x268, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x269, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x26a, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x26b, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x26c, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x26d, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x26e, ignored
qemu-system-i386: NVMM: Unexpected RDMSR 0x26f, ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x250 [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x258 [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x259 [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x268 [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x269 [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x26a [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x26b [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x26c [val=0x0], ignored
qemu-system-i386: NVMM: Unexpected WRMSR 0x26d [val=0x0], ignored

https://releng.netbsd.org/b5reports/i386/2025/2025.10.19.20.52.09/install.log

Looks like these are MTRR-related MSRs:

   1322 #define MSR_MTRRfix64K_00000	0x250
   1323 #define MSR_MTRRfix16K_80000	0x258
   1324 #define MSR_MTRRfix16K_A0000	0x259
   1325 #define MSR_MTRRfix4K_C0000	0x268
   1326 #define MSR_MTRRfix4K_C8000	0x269
   1327 #define MSR_MTRRfix4K_D0000	0x26a
   1328 #define MSR_MTRRfix4K_D8000	0x26b
   1329 #define MSR_MTRRfix4K_E0000	0x26c
   1330 #define MSR_MTRRfix4K_E8000	0x26d
   1331 #define MSR_MTRRfix4K_F0000	0x26e
   1332 #define MSR_MTRRfix4K_F8000	0x26f

https://nxr.netbsd.org/xref/src/sys/arch/x86/include/specialreg.h?r=1.220#1322
>How-To-Repeat:
boot NetBSD/x86 under qemu -accel nvmm
>Fix:
Yes, please!

We should be able to handle our own MSR probes as a guest in our flagship hypervisor.  If the MTRR MSRs aren't relevant perhaps we can put in stubs that at least don't print anything.

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