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| author | Hou Wenlong <houwenlong93@linux.alibaba.com> | 2021-11-02 17:15:32 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-03-08 19:12:35 +0100 |
| commit | 1adfbfaeb20d5c2f51348381022c35b906d6c6eb (patch) | |
| tree | de5794052f080183db5556f7de3779d8a0af973d /arch | |
| parent | 3d8468045e39ecb2402b9e54e2d8f5bc6dda5e02 (diff) | |
KVM: x86: Exit to userspace if emulation prepared a completion callback
[ Upstream commit adbfb12d4c4517a8adde23a7fc46538953d56eea ]
em_rdmsr() and em_wrmsr() return X86EMUL_IO_NEEDED if MSR accesses
required an exit to userspace. However, x86_emulate_insn() doesn't return
X86EMUL_*, so x86_emulate_instruction() doesn't directly act on
X86EMUL_IO_NEEDED; instead, it looks for other signals to differentiate
between PIO, MMIO, etc. causing RDMSR/WRMSR emulation not to
exit to userspace now.
Nevertheless, if the userspace_msr_exit_test testcase in selftests
is changed to test RDMSR/WRMSR with a forced emulation prefix,
the test passes. What happens is that first userspace exit
information is filled but the userspace exit does not happen.
Because x86_emulate_instruction() returns 1, the guest retries
the instruction---but this time RIP has already been adjusted
past the forced emulation prefix, so the guest executes RDMSR/WRMSR
and the userspace exit finally happens.
Since the X86EMUL_IO_NEEDED path has provided a complete_userspace_io
callback, x86_emulate_instruction() can just return 0 if the
callback is not NULL. Then RDMSR/WRMSR instruction emulation will
exit to userspace directly, without the RDMSR/WRMSR vmexit.
Fixes: 1ae099540e8c7 ("KVM: x86: Allow deflecting unknown MSR accesses to user space")
Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <56f9df2ee5c05a81155e2be366c9dc1f7adc8817.1635842679.git.houwenlong93@linux.alibaba.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/x86.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6b76486702de..8213f7fb71a7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8068,6 +8068,9 @@ restart: writeback = false; r = 0; vcpu->arch.complete_userspace_io = complete_emulated_mmio; + } else if (vcpu->arch.complete_userspace_io) { + writeback = false; + r = 0; } else if (r == EMULATION_RESTART) goto restart; else |