[PATCH v2 0/3] KVM: SEV: Add support for BTB Isolation

[Kim Phillips]

This feature ensures SNP guest Branch Target Buffers (BTBs) are not
affected by context outside that guest.

The first patch fixes a longstanding bug where users weren't able
to force Automatic IBRS on SNP enabled machines using spectre_v2=eibrs.

The second patch fixes another longstanding bug where users couldn't
select legacy / toggling SPEC_CTRL[IBRS] on AMD systems.  Users of
the BTB Isolation feature may use IBRS to mitigate possible
performance degradation caused by BTB Isolation.

The third patch adds support for the feature by adding it to the
supported features bitmask.

Based on tip/master, currently 7726ce228780.
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

This series also available here:

https://github.com/AMDESE/linux/tree/btb-isol-latest

Advance qemu bits (to add btb-isol=on/off switch) available here:

https://github.com/AMDESE/qemu/tree/btb-isol-latest

Qemu bits will be posted upstream once kernel bits are merged.
They depend on Naveen Rao's "target/i386: SEV: Add support for
enabling VMSA SEV features":

https://lore.kernel.org/qemu-devel/cover.1761648149.git.naveen@xxxxxxxxxx/

v2:
 - Patch 1/3:
   - Address Dave Hansen's comment to adhere to using the IBRS_ENHANCED
     Intel feature flag also for AutoIBRS.

v1:
 https://lore.kernel.org/kvm/20260224180157.725159-1-kim.phillips@xxxxxxx/

Kim Phillips (3):
  cpu/bugs: Allow forcing Automatic IBRS with SNP enabled using
    spectre_v2=eibrs
  cpu/bugs: Allow spectre_v2=ibrs on x86 vendors other than Intel
  KVM: SEV: Add support for SNP BTB Isolation

 arch/x86/include/asm/svm.h   |  1 +
 arch/x86/kernel/cpu/bugs.c   | 19 +++++++++++--------
 arch/x86/kernel/cpu/common.c |  6 +-----
 arch/x86/kvm/svm/sev.c       |  3 +++
 4 files changed, 16 insertions(+), 13 deletions(-)


base-commit: 7726ce2287804e70b2bf2fc00f104530b603d3f3
-- 
2.43.0