This is a note to let you know that I've just added the patch titled
KVM: x86: Don't WARN if userspace mucks with RCX during string I/O exit
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-x86-don-t-warn-if-userspace-mucks-with-rcx-during-string-i-o-exit.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From d07898eaf39909806128caccb6ebd922ee3edd69 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Mon, 25 Oct 2021 13:13:10 -0700
Subject: KVM: x86: Don't WARN if userspace mucks with RCX during string I/O exit
From: Sean Christopherson <seanjc@xxxxxxxxxx>
commit d07898eaf39909806128caccb6ebd922ee3edd69 upstream.
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@xxxxxxxxxxxxxxx
Fixes: 3b27de271839 ("KVM: x86: split the two parts of emulator_pio_in")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20211025201311.1881846-2-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7021,7 +7021,13 @@ static int emulator_pio_in(struct kvm_vc
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)
@@ -7030,7 +7036,6 @@ static int emulator_pio_in(struct kvm_vc
/* Results already available, fall through. */
}
- WARN_ON(count != vcpu->arch.pio.count);
complete_emulator_pio_in(vcpu, val);
return 1;
}
Patches currently in stable-queue which might be from seanjc@xxxxxxxxxx are
queue-5.15/kvm-x86-ignore-sparse-banks-size-for-an-all-cpus-non-sparse-ipi-req.patch
queue-5.15/kvm-x86-don-t-warn-if-userspace-mucks-with-rcx-during-string-i-o-exit.patch
