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From:   Ramakrishna Saripalli <rsaripal@amd.com>
To:     <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>
CC:     <rsaripal@amd.com>
Subject: [PATCH 5/5] x86/speculation: Add PSF mitigation kernel parameters
Date:   Tue, 6 Apr 2021 10:50:04 -0500
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From: Ramakrishna Saripalli <rk.saripalli@amd.com>

PSF mitigation introduces new kernel parameters.

The kernel parameters for PSF mitigation are modeled
after spec_store_bypass_disable.

Signed-off-by: Ramakrishna Saripalli<rk.saripalli@amd.com>
---
 .../admin-guide/kernel-parameters.txt         | 45 +++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 04545725f187..68dfde77a87d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2876,6 +2876,7 @@
 					       nospectre_v2 [X86,PPC,S390,ARM64]
 					       spectre_v2_user=off [X86]
 					       spec_store_bypass_disable=off [X86,PPC]
+					       psfd=off [X86]
 					       ssbd=force-off [ARM64]
 					       l1tf=off [X86]
 					       mds=off [X86]
@@ -3243,6 +3244,8 @@
 
 	nohugeiomap	[KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
 
+	nopsfd          [HW,X86] Disable mitigation for Predictive Store Forwarding.
+
 	nosmt		[KNL,S390] Disable symmetric multithreading (SMT).
 			Equivalent to smt=1.
 
@@ -4002,6 +4005,48 @@
 			that).
 			Format: <bool>
 
+        psfd=		[HW,X86]
+                        Predictive Store Forwarding Disable control
+
+                        Certain AMD processors feature a new technology called Predictive
+                        Store Forwarding. This feature is designed to improve the
+                        performance of code execution by predicting dependencies
+                        between loads and stores.
+
+                        Modern processors implement techniques to optimize the
+                        execution of a load instruction to an address that was
+                        recently written by a store instruction.
+
+                        PSF expands on the above by speculating on the relationship
+                        between loads and stores without waiting for address
+                        calculation to complete. With PSF, CPU learns over time the
+                        relationship between loads and stores.
+
+                        Incorrect PSF predictions can occur for various reasons.
+                        Please see the AMD PSF whitepaper for more information.
+
+                        All AMD processors that implement PSF also provide ability
+                        to control mitigation of PSF.
+
+                        Following options are provided to control PSF mitigation.
+
+                        The options are:
+                        on      - Unconditionally disable Speculative Store Bypass
+                        off     - Unconditionally enable Speculative Store Bypass
+                        auto    - Kernel detects whether the CPU is vulnerable.
+                                  If the CPU is not vulnerable, off is selected.
+                                  If the CPU is vulnerable, default mitigation is
+                                  KConfig dependent.
+                        prctl   - Control Predictive Store Forwarding per thread
+                                  via prctl. Predictive Store Forwarding is enabled
+                                  per process by default. The state of the control
+                                  is inherited on fork.
+                        seccomp - Same as prctl above but all seccomp threads will
+                                  disable PSF unless they opt out.
+
+                        Default mitigations:
+                        [X86] If CONFIG_SECCOMP=y "seccomp" else "prctl"
+
 	psi=		[KNL] Enable or disable pressure stall information
 			tracking.
 			Format: <bool>
-- 
2.25.1