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Date: Tue, 7 Sep 2021 14:36:21 +0800 From: Hao Peng <flyingpenghao@...il.com> To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> Cc: tglx@...utronix.de, mingo@...hat.com, Borislav Petkov <bp@...en8.de>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] x86/tsx: clear RTM and HLE when MSR_IA32_TSX_CTRL is not supported On Tue, Sep 7, 2021 at 1:13 PM Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote: > > On 06.09.2021 10:46, Hao Peng wrote: > >If hypervisor does not support MSR_IA32_TSX_CTRL, but guest supports > >RTM and HLE features, it will affect TAA mitigation. > > Guests are on purpose not allowed to control TSX via MSR_IA32_TSX_CTRL, > otherwise a malicious guest can enable TSX and attack host or other > guests. The TAA mitigation within a guest is same as MDS i.e. > micro-architectural buffer clear using VERW instruction. Support for > VERW is added by the microcode update and enumerate by > MSR_ARCH_CAP[MD_CLEAR] bit. > > >Signed-off-by: Peng Hao <flyingpeng@...cent.com> > >--- > > arch/x86/kernel/cpu/tsx.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > >diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c > >index 9c7a5f049292..5e852c14fef2 100644 > >--- a/arch/x86/kernel/cpu/tsx.c > >+++ b/arch/x86/kernel/cpu/tsx.c > >@@ -122,6 +122,13 @@ void __init tsx_init(void) > > > > if (!tsx_ctrl_is_supported()) { > > tsx_ctrl_state = TSX_CTRL_NOT_SUPPORTED; > >+ > >+ /* If hypervisor does not support MSR_IA32_TSX_CTRL emulation, > >+ * but guest supports RTM and HLE features, it will affect TAA > >+ * (tsx_async_abort)mitigation. > >+ */ > >+ setup_clear_cpu_cap(X86_FEATURE_RTM); > >+ setup_clear_cpu_cap(X86_FEATURE_HLE); > > This is not correct. TSX feature can exist without TSX_CTRL MSR. > Moreover, clearing the cached bits with setup_clear_cpu_cap() doesn't > disable the TSX feature in CPU. > After applying this patch, the output of /sys/devices/system/cpu/vulnerabilities/tsx_async_abort becomes “Mitigation: TSX disabled”.Do you mean that tsx is still enabled in this case in guest? I made a mistake in the description before. This problem occurred under the qemu -cpu Icelake-server . When I debug this problem to -cpu host, the guest can see taa-no. Thanks. > Thanks, > Pawan
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