SEV-ES and SNP guests fail to boot when FRED is enabled due to missing #VC
exception handling and a CR-pinning issue that prematurely enables FRED before
its MSRs are configured.

Patch 1 fixes the implicit FSGSBASE dependency by moving FSGSBASE enablement
to cpu_init_exception_handling(), ensuring it's enabled before exception
handling infrastructure is set up on both boot and secondary CPUs.

Patch 2 fixes the CR-pinning issue by deferring enforcement during secondary
CPU bringup, preventing FRED from being enabled before it is configured and
able to handle exceptions.

Patch 3 adds #VC exception handling to FRED and fixes early GHCB access to
use boot_ghcb before per-CPU GHCBs are initialized.

These fixes enable SEV-ES/SNP guests to boot successfully with FRED enabled.

Changelog:
v2 -> v3:
* Fix SNP guest boot failure reported by Borislav Petkov - the CR pinning
  disable patch exposed an implicit FSGSBASE dependency that is now fixed
  by moving FSGSBASE enablement to cpu_init_exception_handling() (Boris/Sohil)

v1 -> v2:
https://lore.kernel.org/kvm/20260226092349.803491-1-nikunj@amd.com/
* Instead of moving pr_info(), fix the root cause by disabling CR pinning
  during secondary CPU bringup (Dave Hansen)
* Use unified #VC exception handler in fred_hwexc() (Dave Hansen)
* Collect RoB (Sohil Mehta)

v1: https://lore.kernel.org/kvm/20260205051030.1225975-1-nikunj@amd.com/

Dave Hansen (1):
  x86/cpu: Disable CR pinning during CPU bringup

Nikunj A Dadhania (2):
  x86/cpu: Enable FSGSBASE early in cpu_init_exception_handling()
  x86/fred: Fix early boot failures on SEV-ES/SNP guests

 arch/x86/coco/sev/noinstr.c  |  6 ++++++
 arch/x86/entry/entry_fred.c  | 14 ++++++++++++
 arch/x86/kernel/cpu/common.c | 41 +++++++++++++++++++++++++++---------
 3 files changed, 51 insertions(+), 10 deletions(-)


base-commit: 270b06a2452b0a20b149591ee90e22e3d8d55358
-- 
2.48.1

On Wed, Mar 18, 2026 at 07:56:51AM +0000, Nikunj A Dadhania wrote:
> Dave Hansen (1):
>   x86/cpu: Disable CR pinning during CPU bringup
> 
> Nikunj A Dadhania (2):
>   x86/cpu: Enable FSGSBASE early in cpu_init_exception_handling()
>   x86/fred: Fix early boot failures on SEV-ES/SNP guests
> 
>  arch/x86/coco/sev/noinstr.c  |  6 ++++++
>  arch/x86/entry/entry_fred.c  | 14 ++++++++++++
>  arch/x86/kernel/cpu/common.c | 41 +++++++++++++++++++++++++++---------
>  3 files changed, 51 insertions(+), 10 deletions(-)

Looks good so far in testing, I'll hammer on it some more and then queue it
later.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette