KVM: VMX: Add a trampoline to fix VMREAD error handling

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Add a hand coded assembly trampoline to preserve volatile registers
across vmread_error(), and to handle the calling convention differences
between 64-bit and 32-bit due to asmlinkage on vmread_error().  Pass
@field and @fault on the stack when invoking the trampoline to avoid
clobbering volatile registers in the context of the inline assembly.

Calling vmread_error() directly from inline assembly is partially broken
on 64-bit, and completely broken on 32-bit.  On 64-bit, it will clobber
%rdi and %rsi (used to pass @field and @fault) and any volatile regs
written by vmread_error().  On 32-bit, asmlinkage means vmread_error()
expects the parameters to be passed on the stack, not via regs.

Opportunistically zero out the result in the trampoline to save a few
bytes of code for every VMREAD.  A happy side effect of the trampoline
is that the inline code footprint is reduced by three bytes on 64-bit
due to PUSH/POP being more efficent (in terms of opcode bytes) than MOV.

Fixes: 6e2020977e ("KVM: VMX: Add error handling to VMREAD helper")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200326160712.28803-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2020-03-26 09:07:12 -07:00 • committed by Paolo Bonzini

parent 9c14ee21fc

commit 842f4be958

2 changed files with 79 additions and 7 deletions

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28

arch/x86/kvm/vmx/ops.h

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58

arch/x86/kvm/vmx/vmenter.S

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