Re: [PATCH 0/8] KVM: SVM: Clean up VMRUN=>#VMEXIT assembly

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On 2/23/24 14:42, Sean Christopherson wrote:
Clean up SVM's enter/exit assembly code so that it can be compiled
without OBJECT_FILES_NON_STANDARD.  The "standard" __svm_vcpu_run() can't
be made 100% bulletproof, as RBP isn't restored on #VMEXIT, but that's
also the case for __vmx_vcpu_run(), and getting "close enough" is better
than not even trying.

As for SEV-ES, after yet another refresher on swap types, I realized KVM
can simply let the hardware restore registers after #VMEXIT, all that's
missing is storing the current values to the host save area (I learned the
hard way that they are swap Type B, *sigh*).  Unless I'm missing something,
this provides 100% accuracy when using stack frames for unwinding, and
requires less assembly (though probably not fewer code bytes; I didn't check).

In between, build the SEV-ES code iff CONFIG_KVM_AMD_SEV=y, and yank out
"support" for 32-bit kernels, which was unncessarily polluting the code.

I'm pretty sure I actually managed to test all of this, thanks to the SEV-ES
smoke selftests, and a bit of hacking to disable V_SPEC_CTRL, passthrough
SPEC_CTRL unconditionally, and have the selftests W/R SPEC_CTRL from its

Sean Christopherson (8):
   KVM: SVM: Create a stack frame in __svm_vcpu_run() for unwinding
   KVM: SVM: Wrap __svm_sev_es_vcpu_run() with #ifdef CONFIG_KVM_AMD_SEV
   KVM: SVM: Drop 32-bit "support" from __svm_sev_es_vcpu_run()
   KVM: SVM: Clobber RAX instead of RBX when discarding
   KVM: SVM: Save/restore non-volatile GPRs in SEV-ES VMRUN via host save
   KVM: SVM: Save/restore args across SEV-ES VMRUN via host save area
   KVM: SVM: Create a stack frame in __svm_sev_es_vcpu_run()
   KVM: x86: Stop compiling vmenter.S with OBJECT_FILES_NON_STANDARD

  arch/x86/kvm/Makefile      |  4 --
  arch/x86/kvm/svm/svm.c     | 17 ++++---
  arch/x86/kvm/svm/svm.h     |  3 +-
  arch/x86/kvm/svm/vmenter.S | 97 +++++++++++++++++---------------------
  4 files changed, 56 insertions(+), 65 deletions(-)

Nice cleanup, thanks!

For the series:
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

base-commit: ec1e3d33557babed2c2c2c7da6e84293c2f56f58

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