[PATCH 3/4] x86/speculation: Implement PSF mitigation support

[Ramakrishna Saripalli <rsaripal@amd.com>]

From: Ramakrishna Saripalli <rk.saripalli@amd.com>

Implement support for PSF mitigation via a kernel parameter.

Kernel parameter predict_store_fwd has the following values

- off. PSF mitigation is enabled which means the feature is disabled.

- on. PSF mitigation is not enabled. This is also the default behavior.

Signed-off-by: Ramakrishna Saripalli<rk.saripalli@amd.com>
---
 arch/x86/kernel/cpu/amd.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 347a956f71ca..88aac52eeb1b 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1170,3 +1170,22 @@ void set_dr_addr_mask(unsigned long mask, int dr)
 		break;
 	}
 }
+
+static int __init psf_cmdline(char *str)
+{
+	if (!boot_cpu_has(X86_FEATURE_PSFD))
+		return 0;
+
+	if (!str)
+		return -EINVAL;
+
+	if (!strcmp(str, "off")) {
+		x86_spec_ctrl_base |= SPEC_CTRL_PSFD;
+		wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+		setup_clear_cpu_cap(X86_FEATURE_PSFD);
+	}
+
+	return 0;
+}
+
+early_param("predict_store_fwd", psf_cmdline);
-- 
2.25.1