58 lines
2.1 KiB
Diff
58 lines
2.1 KiB
Diff
From: speck for Pawan Gupta <speck@linutronix.de>
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Date: Wed, 9 Oct 2019 16:27:56 -0700
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Subject: TAAv6 6
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Export IA32_ARCH_CAPABILITIES MSR bit MDS_NO=0 to guests on TSX Async
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Abort(TAA) affected hosts that have TSX enabled and updated microcode.
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This is required so that the guests don't complain,
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"Vulnerable: Clear CPU buffers attempted, no microcode"
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when the host has the updated microcode to clear CPU buffers.
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Microcode update also adds support for MSR_IA32_TSX_CTRL which is
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enumerated by the ARCH_CAP_TSX_CTRL bit in IA32_ARCH_CAPABILITIES MSR.
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Guests can't do this check themselves when the ARCH_CAP_TSX_CTRL bit is
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not exported to the guests.
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In this case export MDS_NO=0 to the guests. When guests have
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CPUID.MD_CLEAR=1 guests deploy MDS mitigation which also mitigates TAA.
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Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
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Reviewed-by: Tony Luck <tony.luck@intel.com>
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Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
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---
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arch/x86/kvm/x86.c | 19 +++++++++++++++++++
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1 file changed, 19 insertions(+)
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index 1ecadf51f154..5ccf79739b2b 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -1143,6 +1143,25 @@ u64 kvm_get_arch_capabilities(void)
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if (l1tf_vmx_mitigation != VMENTER_L1D_FLUSH_NEVER)
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data |= ARCH_CAP_SKIP_VMENTRY_L1DFLUSH;
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+ /*
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+ * On TAA affected systems, export MDS_NO=0 when:
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+ * - TSX is enabled on host, i.e. X86_FEATURE_RTM=1.
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+ * - Updated microcode is present. This is detected by
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+ * the presence of ARCH_CAP_TSX_CTRL_MSR. This ensures
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+ * VERW clears CPU buffers.
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+ *
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+ * When MDS_NO=0 is exported, guests deploy clear CPU buffer
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+ * mitigation and don't complain:
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+ *
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+ * "Vulnerable: Clear CPU buffers attempted, no microcode"
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+ *
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+ * If TSX is disabled on the system, guests are also mitigated against
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+ * TAA and clear CPU buffer mitigation is not required for guests.
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+ */
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+ if (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM) &&
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+ (data & ARCH_CAP_TSX_CTRL_MSR))
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+ data &= ~ARCH_CAP_MDS_NO;
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+
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return data;
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}
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EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
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