ACK/Cmnt: [SRU][Q/N/J:linux-azure][PATCH 0/2] [Azure] AMDv4 VMs may get no timer interrupts or suffer from timer interrupt storms

[Benjamin Wheeler]

Note to applier, please make the following change in [SRU][J:linux-azure][PATCH
2/6] clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to avoid special
casing U64_MAX
<http://ktml-board.kernel/archive/20260120191555.1321209-5-john.cabaj@canonical.com/>
:

Change
> (backported picked from commit 9397fa2ea3e7634f61da1ab76b9eb88ba04dfdfc)
to
> (backported from commit 9397fa2ea3e7634f61da1ab76b9eb88ba04dfdfc)

John, let me know if I mixed those two up.

Acked-by: Benjamin Wheeler <benjamin.wheeler at canonical.com>

On Tue, Jan 20, 2026 at 2:16 PM John Cabaj <john.cabaj at canonical.com> wrote:
>
> BugLink: https://bugs.launchpad.net/bugs/2137674
>
> SRU Justification
>
> [Impact]
>
> * Microsoft requested patches to work around intermittent deployment
failures on AMDv4 VM sizes due to issues with large values of Hyper-V timer
>
> [Fix]
>
> * Questing and Noble:
> - cherry-picks of the following SAUCE patches from Microsoft (
https://github.com/dcui/linux/tree/decui/Ubuntu-azure-6.8-6.8.0-1043.49_22.04.1-V2
):
>   - 28b18cb: "UBUNTU: SAUCE: clocksource: hyper-v: do not use an insanely
big TSC in hv_read_tsc_page_tsc()"
>   - f796530: "UBUNTU: SAUCE: clocksource: hyper-v: use the APIC timer if
the Hyper-V timer is unreliable on some CPUs"
> * Jammy:
> - cherry-pick of the following SAUCE patch from Microsoft (
https://github.com/dcui/linux/tree/decui/Ubuntu-azure-6.8-6.8.0-1043.49_22.04.1-V2
):
>   - 28b18cb: "UBUNTU: SAUCE: clocksource: hyper-v: do not use an insanely
big TSC in hv_read_tsc_page_tsc()"
> - backport of the following SAUCE patch from Microsoft (
https://github.com/dcui/linux/tree/decui/Ubuntu-azure-6.8-6.8.0-1043.49_22.04.1-V2
):
>   - f796530: "UBUNTU: SAUCE: clocksource: hyper-v: use the APIC timer if
the Hyper-V timer is unreliable on some CPUs"
> - cherry-pick of the following upstream patches
>   - fd0c6b0: "x86/vdso: Fix gettimeofday masking"
>   - 4b52223: "clocksource: hyper-v: Provide noinstr sched_clock()"
> - backports of the following upstream patches
>   - 9dfb6bf: "clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to
avoid special casing U64_MAX"
>   - 47a2a14: "clocksource: hyper-v: Introduce a pointer to TSC page"
>
> [Test Plan]
>
> * Compile tested
> * Microsoft tested
>
> [Regression potential]
>
> * Upstream changes are largely localized to time and clock source
functions, and have been upstream for some time. Regression likliehood is
slim.
> * Possible regressions could result in unexpected behavior of Hyper-V
driver.
>
> [Other info]
>
> * SF#00422328
>
> Dexuan Cui (2):
>   UBUNTU: SAUCE: clocksource: hyper-v: do not use an insanely big TSC in
>     hv_read_tsc_page_tsc()
>   UBUNTU: SAUCE: clocksource: hyper-v: use the APIC timer if the Hyper-V
>     timer is unreliable on some CPUs
>
>  arch/x86/kernel/cpu/mshyperv.c     | 43 ++++++++++++++++++++++++++++++
>  drivers/clocksource/hyperv_timer.c |  4 ++-
>  include/clocksource/hyperv_timer.h |  4 +++
>  3 files changed, 50 insertions(+), 1 deletion(-)
>
> --
> 2.43.0
>
>
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
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