[xen staging] x86/boot: Further simplify CR4 handling in dom0_construct_pv()

[patchbot@xxxxxxx]

commit 4c21b6affb4c5a3afe22cbc144362091de063366
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Aug 30 18:49:53 2024 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Oct 18 11:30:34 2024 +0100

    x86/boot: Further simplify CR4 handling in dom0_construct_pv()
    
    The logic would be more robust disabling SMAP based on its precense in CR4,
    rather than SMAP's accociation with a synthetic feature.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/pv/dom0_build.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 262edb6bf2..ee9ecdc2ab 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -1057,6 +1057,7 @@ int __init dom0_construct_pv(struct domain *d,
                              module_t *initrd,
                              const char *cmdline)
 {
+    unsigned long cr4 = read_cr4();
     int rc;
 
     /*
@@ -1064,19 +1065,19 @@ int __init dom0_construct_pv(struct domain *d,
      * prevents us needing to write construct_dom0() in terms of
      * copy_{to,from}_user().
      */
-    if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) )
+    if ( cr4 & X86_CR4_SMAP )
     {
         if ( IS_ENABLED(CONFIG_PV32) )
             cr4_pv32_mask &= ~X86_CR4_SMAP;
 
-        write_cr4(read_cr4() & ~X86_CR4_SMAP);
+        write_cr4(cr4 & ~X86_CR4_SMAP);
     }
 
     rc = dom0_construct(d, image, image_headroom, initrd, cmdline);
 
-    if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) )
+    if ( cr4 & X86_CR4_SMAP )
     {
-        write_cr4(read_cr4() | X86_CR4_SMAP);
+        write_cr4(cr4);
 
         if ( IS_ENABLED(CONFIG_PV32) )
             cr4_pv32_mask |= X86_CR4_SMAP;
--
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