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From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: speck@linutronix.de
Subject: [MODERATED] [PATCH v6 6/9] TAAv6 6
Date: Wed, 9 Oct 2019 16:27:56 -0700	[thread overview]
Message-ID: <=?utf-8?q?=3C17abe51f7bde1193efa4c5450f51a247ae39aaaa=2E157065?= =?utf-8?q?8889=2Egit=2Epawan=2Ekumar=2Egupta=40linux=2Eintel=2Ecom=3E?=> (raw)
In-Reply-To: <cover.1570658888.git.pawan.kumar.gupta@linux.intel.com>

Export IA32_ARCH_CAPABILITIES MSR bit MDS_NO=0 to guests on TSX Async
Abort(TAA) affected hosts that have TSX enabled and updated microcode.
This is required so that the guests don't complain,

	"Vulnerable: Clear CPU buffers attempted, no microcode"

when the host has the updated microcode to clear CPU buffers.

Microcode update also adds support for MSR_IA32_TSX_CTRL which is
enumerated by the ARCH_CAP_TSX_CTRL bit in IA32_ARCH_CAPABILITIES MSR.
Guests can't do this check themselves when the ARCH_CAP_TSX_CTRL bit is
not exported to the guests.

In this case export MDS_NO=0 to the guests. When guests have
CPUID.MD_CLEAR=1 guests deploy MDS mitigation which also mitigates TAA.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
---
 arch/x86/kvm/x86.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 91602d310a3f..282b909b9394 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1254,6 +1254,25 @@ static u64 kvm_get_arch_capabilities(void)
 	if (l1tf_vmx_mitigation != VMENTER_L1D_FLUSH_NEVER)
 		data |= ARCH_CAP_SKIP_VMENTRY_L1DFLUSH;
 
+	/*
+	 * On TAA affected systems, export MDS_NO=0 when:
+	 *	- TSX is enabled on host, i.e. X86_FEATURE_RTM=1.
+	 *	- Updated microcode is present. This is detected by
+	 *	  the presence of ARCH_CAP_TSX_CTRL_MSR. This ensures
+	 *	  VERW clears CPU buffers.
+	 *
+	 * When MDS_NO=0 is exported, guests deploy clear CPU buffer
+	 * mitigation and don't complain:
+	 *
+	 *	"Vulnerable: Clear CPU buffers attempted, no microcode"
+	 *
+	 * If TSX is disabled on the system, guests are also mitigated against
+	 * TAA and clear CPU buffer mitigation is not required for guests.
+	 */
+	if (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM) &&
+	    (data & ARCH_CAP_TSX_CTRL_MSR))
+		data &= ~ARCH_CAP_MDS_NO;
+
 	return data;
 }
 
-- 
2.20.1

  parent reply	other threads:[~2019-10-09 23:33 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09 23:21 [MODERATED] [PATCH v6 0/9] TAAv6 0 Pawan Gupta
2019-10-09 23:22 ` [MODERATED] [PATCH v6 1/9] TAAv6 1 Pawan Gupta
2019-10-09 23:23 ` [MODERATED] [PATCH v6 2/9] TAAv6 2 Pawan Gupta
2019-10-09 23:24 ` [MODERATED] [PATCH v6 3/9] TAAv6 3 Pawan Gupta
2019-10-09 23:25 ` [MODERATED] [PATCH v6 4/9] TAAv6 4 Pawan Gupta
2019-10-09 23:26 ` [MODERATED] [PATCH v6 5/9] TAAv6 5 Pawan Gupta
2019-10-09 23:27 ` Pawan Gupta [this message]
2019-10-09 23:28 ` [MODERATED] [PATCH v6 7/9] TAAv6 7 Pawan Gupta
2019-10-09 23:29 ` [MODERATED] [PATCH v6 8/9] TAAv6 8 Pawan Gupta
2019-10-09 23:30 ` [MODERATED] [PATCH v6 9/9] TAAv6 9 Pawan Gupta
2019-10-09 23:34 ` [MODERATED] Re: [PATCH v6 1/9] TAAv6 1 Pawan Gupta
2019-10-10  1:23   ` Pawan Gupta
2019-10-15 12:54     ` Thomas Gleixner
2019-10-21 20:35       ` [MODERATED] " Pawan Gupta
2019-10-09 23:38 ` Andrew Cooper
2019-10-09 23:40   ` Andrew Cooper
2019-10-09 23:53     ` Luck, Tony
2019-10-10  0:01       ` Andrew Cooper
2019-10-10 16:51         ` Luck, Tony
     [not found] ` <5d9e6daa.1c69fb81.f84ad.88ceSMTPIN_ADDED_BROKEN@mx.google.com>
2019-10-10  6:47   ` [MODERATED] Re: [PATCH v6 3/9] TAAv6 3 Greg KH
2019-10-10 23:44     ` Pawan Gupta
     [not found] ` <5d9e6e22.1c69fb81.6df19.ff55SMTPIN_ADDED_BROKEN@mx.google.com>
2019-10-10  6:50   ` [MODERATED] Re: [PATCH v6 5/9] TAAv6 5 Greg KH
2019-10-10 21:18     ` Pawan Gupta
2019-10-10  6:50   ` Greg KH
     [not found] ` <5d9e6f13.1c69fb81.d7036.be99SMTPIN_ADDED_BROKEN@mx.google.com>
2019-10-10  6:54   ` [MODERATED] Re: [PATCH v6 9/9] TAAv6 9 Greg KH
2019-10-12  1:41     ` Pawan Gupta
2019-10-13 20:05       ` Ben Hutchings
2019-10-13 21:00         ` Ben Hutchings
     [not found] ` <4b15283c29b75be3177eb7c4b8601be5644f630e.157065=?utf-8?q?8889?= .git.pawan.kumar.gupta@linux.intel.com>
2019-10-18  1:21   ` [MODERATED] Re: [PATCH v6 8/9] TAAv6 8 Ben Hutchings
2019-10-21 20:04 ` [MODERATED] Re: [PATCH v6 0/9] TAAv6 0 Josh Poimboeuf
2019-10-21 20:09   ` Pawan Gupta

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