Sean Christopherson 32b758d12c KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU ...

[ Upstream commit 6f390916c4 ]

Wrap s390's halt_poll_max_steal with READ_ONCE and snapshot the result of
kvm_arch_no_poll() in kvm_vcpu_block() to avoid a mostly-theoretical,
largely benign bug on s390 where the result of kvm_arch_no_poll() could
change due to userspace modifying halt_poll_max_steal while the vCPU is
blocking.  The bug is largely benign as it will either cause KVM to skip
updating halt-polling times (no_poll toggles false=>true) or to update
halt-polling times with a slightly flawed block_ns.

Note, READ_ONCE is unnecessary in the current code, add it in case the
arch hook is ever inlined, and to provide a hint that userspace can
change the param at will.

Fixes: 8b905d28ee ("KVM: s390: provide kvm_arch_no_poll function")
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

2022-03-08 19:12:34 +01:00

..

kvm

KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU

2022-03-08 19:12:34 +01:00

lib

Revert "irqbypass: do not start cons/prod when failed connect"

2021-05-15 10:26:55 +01:00

Makefile

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