[26.04_linux-nvidia] Backport removal of extra ISBs when using msr_hcr_el2

[esot0]

Backport of 54a3cc145456272b10c1452fe89e1dcf933d5c39, which removes redundant ISBs after msr_hcr_el2, so HCR_EL2 writes do one barrier instead of two and run a bit faster. Verified that patch is present in kernel using check-hcr-isb.sh.

Script output:

kernel  : 7.0.12+  (running: 7.0.12+)
image   : /boot/vmlinuz-7.0.12+
symbols : /boot/System.map-7.0.12+
erratum : CONFIG_AMPERE_ERRATUM_AC04_CPU_23=y
note    : commit landed in v7.1-rc1; no Cc: stable, so no -stable backport

zstd: /*stdin*\: unsupported format 
image format: compressed Image  (73728000 bytes flat)
_text       : 0xffff800080000000

=== sites generated by the msr_hcr_el2 assembly macro (what the patch touches) ===
vaddr              symbol                                     prev      instr            next      next+1      pattern
--------------------------------------------------------------------------------------------------------------------------------------
0xffff800081a40be0 __kvm_nvhe____kvm_hyp_init+0x18            dsb nsh   msr hcr_el2,x1   isb       0xd2c00082  single-isb
0xffff800081a40cd0 __kvm_nvhe___kvm_hyp_init_cpu+0x40         dsb nsh   msr hcr_el2,x0   isb       0xd2800021  single-isb
0xffff800081a40d04 __kvm_nvhe___kvm_hyp_init_cpu+0x74         dsb nsh   msr hcr_el2,x0   isb       0x97fffead  single-isb
0xffff800081a41ad8 __finalise_el2+0x278                       dsb nsh   msr hcr_el2,x0   isb       0xd53c4100  single-isb
0xffff800082e111a4 init_el2+0x58                              dsb nsh   msr hcr_el2,x0   isb       0xd2800021  single-isb
0xffff800082e111d8 init_el2+0x8c                              dsb nsh   msr hcr_el2,x0   isb       0xd2a00000  single-isb

=== other HCR_EL2 writes: C write_sysreg_hcr(), NOT touched by this patch ===
38 sites (5 of them double-isb) -- expected noise, ignore for the verdict

======================================================================================================================================
CONFIG_AMPERE_ERRATUM_AC04_CPU_23=y -> signature is the double ISB
RESULT: commit 54a3cc145456 IS PRESENT (0/6 macro sites have back-to-back ISBs)
======================================================================================================================================

Launchpad: https://bugs.launchpad.net/ubuntu/+source/linux-nvidia-bos/+bug/2163052

[github-actions]

PR Validation Report

Patchscan ✅ No Missing Fixes

All cherry-picked commits checked — no missing upstream fixes found.

PR Lint ✅ All checks passed

Details

Checking 1 commits...

Cherry-pick digest:
┌──────────────┬──────────────────────────────────────────────────────────────────┬────────────┬─────────┬───────────────────────────┐
│ Local        │ Referenced upstream / Patch subject                              │ Patch-ID   │ Subject │ SoB chain                 │
├──────────────┼──────────────────────────────────────────────────────────────────┼────────────┼─────────┼───────────────────────────┤
│ 3bda771df678 │ 54a3cc145456 KVM: arm64: Remove extra ISBs when using msr_hcr_el │ match      │ match   │ preserved + emilys added  │
└──────────────┴──────────────────────────────────────────────────────────────────┴────────────┴─────────┴───────────────────────────┘

Lint: all checks passed.

[jamieNguyenNVIDIA]

Hi @esot0,

Same comment for this and #534:

This patch picks cleanly, so it should be reported as:

(cherry picked from commit 54a3cc145456272b10c1452fe89e1dcf933d5c39)

rather than:

(backported from commit 54a3cc145456272b10c1452fe89e1dcf933d5c39)

As such, you ought to drop the backport note too:

[emilys: Removes redundant ISBs after msr_hcr_el2, so HCR_EL2 writes do one barrier instead of two and run a bit faster.]

This describes what the upstream patch does rather than what was changed while moving it to this branch. The other bracketed notes on this branch record the adjustment that was made, for example:

  [ltrager: minor merge conflicts]
  [mochs: Minor context adjustment due to absent definitions]

[clsotog]

Acked-by: Carol L Soto <csoto@nvidia.com>

[nvmochs]

LGTM!

Acked-by: Matthew R. Ochs <mochs@nvidia.com>

[jamieNguyenNVIDIA]

Acked-by: Jamie Nguyen <jamien@nvidia.com>

[nvmochs]

Merged, closing PR.

7caa3af067e7 (nresolute/main-next) KVM: arm64: Remove extra ISBs when using msr_hcr_el2