powerpc/powernv: Get STF barrier requirements from device-tree

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

diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
index 378f7e5f18d206d5b65c902adfb685499b10998a..824c3ad7a0fafb650fd4691b935a857d13a7a70d 100644 (file)
--- 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 __init pnv_setup_security_mitigations(void)