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authorSean Christopherson <seanjc@google.com>2021-10-25 13:13:10 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2021-12-10 09:38:02 -0500
commitd07898eaf39909806128caccb6ebd922ee3edd69 (patch)
tree59dcfd2ed145fc9b9706d7c092fd0ee4471ae39e /arch/x86
parent777ab82d7ce0451fd47bb57e331548deba57394e (diff)
KVM: x86: Don't WARN if userspace mucks with RCX during string I/O exit
Replace a WARN with a comment to call out that userspace can modify RCX during an exit to userspace to handle string I/O. KVM doesn't actually support changing the rep count during an exit, i.e. the scenario can be ignored, but the WARN needs to go as it's trivial to trigger from userspace. Cc: stable@vger.kernel.org Fixes: 3b27de271839 ("KVM: x86: split the two parts of emulator_pio_in") Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20211025201311.1881846-2-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kvm/x86.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c473498c8512..0cf1082455df 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7122,7 +7122,13 @@ static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
unsigned short port, void *val, unsigned int count)
{
if (vcpu->arch.pio.count) {
- /* Complete previous iteration. */
+ /*
+ * Complete a previous iteration that required userspace I/O.
+ * Note, @count isn't guaranteed to match pio.count as userspace
+ * can modify ECX before rerunning the vCPU. Ignore any such
+ * shenanigans as KVM doesn't support modifying the rep count,
+ * and the emulator ensures @count doesn't overflow the buffer.
+ */
} else {
int r = __emulator_pio_in(vcpu, size, port, count);
if (!r)
@@ -7131,7 +7137,6 @@ static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
/* Results already available, fall through. */
}
- WARN_ON(count != vcpu->arch.pio.count);
complete_emulator_pio_in(vcpu, val);
return 1;
}