[Xen-devel] [PATCH v2 2/2] x86/xpti: don't map stack guard pages

["Jan Beulich" <JBeulich@xxxxxxxx>]

Other than for the main mappings, don't even do this in release builds,
as there are no huge page shattering concerns here.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: New.

--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -799,7 +799,8 @@ static int setup_cpu_root_pgt(unsigned i
 
     /* Install direct map page table entries for stack, IDT, and TSS. */
     for ( off = rc = 0; !rc && off < STACK_SIZE; off += PAGE_SIZE )
-        rc = clone_mapping(__va(__pa(stack_base[cpu])) + off, rpt);
+        if ( !memguard_is_stack_guard_page(off) )
+            rc = clone_mapping(__va(__pa(stack_base[cpu])) + off, rpt);
 
     if ( !rc )
         rc = clone_mapping(idt_tables[cpu], rpt);
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5576,6 +5576,14 @@ void memguard_unguard_stack(void *p)
                            STACK_SIZE - PRIMARY_STACK_SIZE - IST_MAX * 
PAGE_SIZE);
 }
 
+bool memguard_is_stack_guard_page(unsigned long addr)
+{
+    addr &= STACK_SIZE - 1;
+
+    return addr >= IST_MAX * PAGE_SIZE &&
+           addr < STACK_SIZE - PRIMARY_STACK_SIZE;
+}
+
 void arch_dump_shared_mem_info(void)
 {
     printk("Shared frames %u -- Saved frames %u\n",
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -519,6 +519,7 @@ void memguard_unguard_range(void *p, uns
 
 void memguard_guard_stack(void *p);
 void memguard_unguard_stack(void *p);
+bool __attribute_const__ memguard_is_stack_guard_page(unsigned long addr);
 
 struct mmio_ro_emulate_ctxt {
         unsigned long cr2;




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