From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
Jim Mattson <jmattson@google.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Sasha Levin <sashal@kernel.org>,
kvm@vger.kernel.org
Subject: [PATCH AUTOSEL 4.19 065/167] KVM: VMX: Compare only a single byte for VMCS' "launched" in vCPU-run
Date: Tue, 3 Sep 2019 12:23:37 -0400 [thread overview]
Message-ID: <20190903162519.7136-65-sashal@kernel.org> (raw)
In-Reply-To: <20190903162519.7136-1-sashal@kernel.org>
From: Sean Christopherson <sean.j.christopherson@intel.com>
[ Upstream commit 61c08aa9606d4e48a8a50639c956448a720174c3 ]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/vmx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2e310ea62d609..562f5dc4645b6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10808,7 +10808,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
"mov %%" _ASM_AX", %%cr2 \n\t"
"3: \n\t"
/* Check if vmlaunch of vmresume is needed */
- "cmpl $0, %c[launched](%0) \n\t"
+ "cmpb $0, %c[launched](%0) \n\t"
/* Load guest registers. Don't clobber flags. */
"mov %c[rax](%0), %%" _ASM_AX " \n\t"
"mov %c[rbx](%0), %%" _ASM_BX " \n\t"
--
2.20.1
next prev parent reply other threads:[~2019-09-03 16:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190903162519.7136-1-sashal@kernel.org>
2019-09-03 16:22 ` [PATCH AUTOSEL 4.19 011/167] KVM: x86: hyperv: enforce vp_index < KVM_MAX_VCPUS Sasha Levin
2019-09-03 16:22 ` [PATCH AUTOSEL 4.19 012/167] KVM: x86: hyperv: consistently use 'hv_vcpu' for 'struct kvm_vcpu_hv' variables Sasha Levin
2019-09-03 16:22 ` [PATCH AUTOSEL 4.19 013/167] KVM: x86: hyperv: keep track of mismatched VP indexes Sasha Levin
2019-09-03 16:22 ` [PATCH AUTOSEL 4.19 014/167] KVM: hyperv: define VP assist page helpers Sasha Levin
2019-09-03 16:22 ` [PATCH AUTOSEL 4.19 015/167] x86/kvm/lapic: preserve gfn_to_hva_cache len on cache reinit Sasha Levin
2019-09-03 16:23 ` Sasha Levin [this message]
2019-09-03 16:23 ` [PATCH AUTOSEL 4.19 073/167] x86/kvmclock: set offset for kvm unstable clock Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 092/167] kvm: mmu: Fix overflow on kvm mmu page limit calculation Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 093/167] x86/kvm: move kvm_load/put_guest_xcr0 into atomic context Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 094/167] KVM: x86: Always use 32-bit SMRAM save state for 32-bit kernels Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 115/167] kvm: Check irqchip mode before assign irqfd Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 132/167] KVM: x86: optimize check for valid PAT value Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 133/167] KVM: VMX: Always signal #GP on WRMSR to MSR_IA32_CR_PAT with bad value Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 134/167] KVM: VMX: Fix handling of #MC that occurs during VM-Entry Sasha Levin
2019-09-03 16:24 ` [PATCH AUTOSEL 4.19 135/167] KVM: VMX: check CPUID before allowing read/write of IA32_XSS Sasha Levin
2019-09-03 16:25 ` [PATCH AUTOSEL 4.19 162/167] virtio/s390: fix race on airq_areas[] Sasha Levin
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