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

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Date: Mon, 26 Feb 2024 14:02:32 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Michael Roth <michael.roth@....com>, Alexey Kardashevskiy <aik@....com>
Subject: Re: [PATCH 0/8] KVM: SVM: Clean up VMRUN=>#VMEXIT assembly

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
> guest.
> 
> 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
>      spec_ctrl_intercepted
>    KVM: SVM: Save/restore non-volatile GPRs in SEV-ES VMRUN via host save
>      area
>    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@....com>

> 
> 
> base-commit: ec1e3d33557babed2c2c2c7da6e84293c2f56f58