From d2a3c131981d4498571908df95c3c9393a00adf5 Mon Sep 17 00:00:00 2001
From: Russell Currey <ruscur@russell.cc>
Date: Mon, 4 Apr 2022 20:15:36 +1000
Subject: [PATCH] powerpc/powernv: Get STF barrier requirements from
 device-tree

References: bsc#1188885 ltc#193722 git-fixes
Patch-mainline: v5.19-rc1
Git-commit: d2a3c131981d4498571908df95c3c9393a00adf5

The device-tree property no-need-store-drain-on-priv-state-switch is
equivalent to H_CPU_BEHAV_NO_STF_BARRIER from the
H_CPU_GET_CHARACTERISTICS hcall on pseries.

Since commit 84ed26fd00c5 ("powerpc/security: Add a security feature for
STF barrier") powernv systems with this device-tree property have been
enabling the STF barrier when they have no need for it.  This patch
fixes this by clearing the STF barrier feature on those systems.

Fixes: 84ed26fd00c5 ("powerpc/security: Add a security feature for STF barrier")
Reported-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220404101536.104794-2-ruscur@russell.cc
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/platforms/powernv/setup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c
@@ -102,6 +102,9 @@ static void __init init_fw_feat_flags(struct device_node *np)
 
 	if (fw_feature_is("enabled", "no-need-l1d-flush-kernel-on-user-access", np))
 		security_ftr_clear(SEC_FTR_L1D_FLUSH_UACCESS);
+
+	if (fw_feature_is("enabled", "no-need-store-drain-on-priv-state-switch", np))
+		security_ftr_clear(SEC_FTR_STF_BARRIER);
 }
 
 static void pnv_setup_security_mitigations(void)
-- 
2.35.3