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It is error-prone that code after vmexit cannot access percpu data
because GSBASE has not been restored yet. It forces MSR_IA32_SPEC_CTRL
save/restore to happen very late, after the predictor untraining
sequence, and it gets in the way of return stack depth tracking
(a retbleed mitigation that is in linux-next as of 2022-11-09).
As a first step towards fixing that, move the VMCB VMSAVE/VMLOAD to
assembly, essentially undoing commit fb0c4a4fee5a ("KVM: SVM: move
VMLOAD/VMSAVE to C code", 2021-03-15). The reason for that commit was
that it made it simpler to use a different VMCB for VMLOAD/VMSAVE versus
VMRUN; but that is not a big hassle anymore thanks to the kvm-asm-offsets
machinery and other related cleanups.
The idea on how to number the exception tables is stolen from
a prototype patch by Peter Zijlstra.
Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Link: <https://lore.kernel.org/all/f571e404-e625-bae1-10e9-449b2eb4cbd8@citrix.com/>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Continue moving accesses to struct vcpu_svm to vmenter.S. Reducing the
number of arguments limits the chance of mistakes due to different
registers used for argument passing in 32- and 64-bit ABIs; pushing the
VMCB argument and almost immediately popping it into a different
register looks pretty weird.
32-bit ABI is not a concern for __svm_sev_es_vcpu_run() which is 64-bit
only; however, it will soon need @svm to save/restore SPEC_CTRL so stay
consistent with __svm_vcpu_run() and let them share the same prototype.
No functional change intended.
Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Since registers are reachable through vcpu_svm, and we will
need to access more fields of that struct, pass it instead
of the regs[] array.
No functional change intended.
Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This already removes an ugly #include "" from asm-offsets.c, but
especially it avoids a future error when trying to define asm-offsets
for KVM's svm/svm.h header.
This would not work for kernel/asm-offsets.c, because svm/svm.h
includes kvm_cache_regs.h which is not in the include path when
compiling asm-offsets.c. The problem is not there if the .c file is
in arch/x86/kvm.
Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
