kaiser: disabled on Xen PV

Kaiser cannot be used on paravirtualized MMUs (namely reading and writing CR3).
This does not work with KAISER as the CR3 switch from and to user space PGD
would require to map the whole XEN_PV machinery into both.

More importantly, enabling KAISER on Xen PV doesn't make too much sense, as PV
guests use distinct %cr3 values for kernel and user already.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
index 8600663ded3e40bfd4dfb0ce5199d01993192037..27688548c3eb0443c2b4119bb37673d3986c06ed 100644 (file)
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -263,6 +263,9 @@ void __init kaiser_check_boottime_disable(void)
        char arg[5];
        int ret;
 
+       if (boot_cpu_has(X86_FEATURE_XENPV))
+               goto silent_disable;
+
        ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
        if (ret > 0) {
                if (!strncmp(arg, "on", 2))
@@ -290,6 +293,8 @@ enable:
 
 disable:
        pr_info("Kernel/User page tables isolation: disabled\n");
+
+silent_disable:
        kaiser_enabled = 0;
        setup_clear_cpu_cap(X86_FEATURE_KAISER);
 }