On Thu, Feb 28, 2019 at 06:14:34PM +0000, Suzuki K Poulose wrote:

On 27/02/2019 01:05, Jeremy Linton wrote:

quoted

There are various reasons, including bencmarking, to disable spectrev2
mitigation on a machine. Provide a command-line to do so.

Signed-off-by: Jeremy Linton <redacted>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org

quoted

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 9950bb0cbd52..d2b2c69d31bb 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c

@@ -220,6 +220,14 @@ static void qcom_link_stack_sanitization(void)
  		     : "=&r" (tmp));
  }
+static bool __nospectre_v2;
+static int __init parse_nospectre_v2(char *str)
+{
+	__nospectre_v2 = true;
+	return 0;
+}
+early_param("nospectre_v2", parse_nospectre_v2);
+
  static void
  enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
  {

@@ -231,6 +239,11 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
  	if (!entry->matches(entry, SCOPE_LOCAL_CPU))
  		return;
+	if (__nospectre_v2) {
+		pr_info_once("spectrev2 mitigation disabled by command line option\n");
+		return;
+	}
+

Could we not disable the "cap" altogether instead, rather than disabling the
work around ? Or do we need that information ?

There are a few ideas here but I think we settled on always reporting in
sysfs even if the mitigation is disabled in .config. So I guess we need
the "cap" around for the reporting part.

-- 
Catalin