* FAILED: patch "[PATCH] KVM: VMX: Compare only a single byte for VMCS' "launched" in" failed to apply to 4.9-stable tree
@ 2019-03-22 10:01 gregkh
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From: gregkh @ 2019-03-22 10:01 UTC (permalink / raw)
To: sean.j.christopherson, jmattson, konrad.wilk, pbonzini, stable; +Cc: stable
The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 61c08aa9606d4e48a8a50639c956448a720174c3 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Fri, 25 Jan 2019 07:40:48 -0800
Subject: [PATCH] KVM: VMX: Compare only a single byte for VMCS' "launched" in
vCPU-run
The vCPU-run asm blob does a manual comparison of a VMCS' launched
status to execute the correct VM-Enter instruction, i.e. VMLAUNCH vs.
VMRESUME. The launched flag is a bool, which is a typedef of _Bool.
C99 does not define an exact size for _Bool, stating only that is must
be large enough to hold '0' and '1'. Most, if not all, compilers use
a single byte for _Bool, including gcc[1].
Originally, 'launched' was of type 'int' and so the asm blob used 'cmpl'
to check the launch status. When 'launched' was moved to be stored on a
per-VMCS basis, struct vcpu_vmx's "temporary" __launched flag was added
in order to avoid having to pass the current VMCS into the asm blob.
The new '__launched' was defined as a 'bool' and not an 'int', but the
'cmp' instruction was not updated.
This has not caused any known problems, likely due to compilers aligning
variables to 4-byte or 8-byte boundaries and KVM zeroing out struct
vcpu_vmx during allocation. I.e. vCPU-run accesses "junk" data, it just
happens to always be zero and so doesn't affect the result.
[1] https://gcc.gnu.org/ml/gcc-patches/2000-10/msg01127.html
Fixes: d462b8192368 ("KVM: VMX: Keep list of loaded VMCSs, instead of vcpus")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 95d618045001..fdb6305cc971 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6402,7 +6402,7 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
"mov %%" _ASM_AX", %%cr2 \n\t"
"3: \n\t"
/* Check if vmlaunch or vmresume is needed */
- "cmpl $0, %c[launched](%%" _ASM_CX ") \n\t"
+ "cmpb $0, %c[launched](%%" _ASM_CX ") \n\t"
/* Load guest registers. Don't clobber flags. */
"mov %c[rax](%%" _ASM_CX "), %%" _ASM_AX " \n\t"
"mov %c[rbx](%%" _ASM_CX "), %%" _ASM_BX " \n\t"
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2019-03-22 10:01 FAILED: patch "[PATCH] KVM: VMX: Compare only a single byte for VMCS' "launched" in" failed to apply to 4.9-stable tree gregkh
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