[PATCH 58/65] x86/alternatives: Clear CR4.CET when clearing CR0.WP

[Andrew Cooper]

This allows us to have CET active much earlier in boot.

Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>

Still TODO: Implement alternatives in a way which doesn't depend on clearing
CR0.WP
---
 xen/arch/x86/alternative.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
index 436047abe021..ec24692e9595 100644
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -333,9 +333,13 @@ static int __init cf_check nmi_apply_alternatives(
      */
     if ( !(alt_done & alt_todo) )
     {
-        unsigned long cr0;
+        unsigned long cr0, cr4;
 
         cr0 = read_cr0();
+        cr4 = read_cr4();
+
+        if ( cr4 & X86_CR4_CET )
+            write_cr4(cr4 & ~X86_CR4_CET);
 
         /* Disable WP to allow patching read-only pages. */
         write_cr0(cr0 & ~X86_CR0_WP);
@@ -345,6 +349,9 @@ static int __init cf_check nmi_apply_alternatives(
 
         write_cr0(cr0);
 
+        if ( cr4 & X86_CR4_CET )
+            write_cr4(cr4);
+
         alt_done |= alt_todo;
     }
 
-- 
2.11.0