x86/EFI: meet further spec requirements for runtime calls

So far we didn't guarantee 16-byte alignment of the stack: While (so
far) we don't tell the compiler to use smaller alignment, we also don't
guarantee 16-byte alignment when establishing stack pointers for new
vCPU-s. Runtime service functions using SSE instructions may end with

Note that -mpreferred-stack-boundary=3 is can be used only from gcc 4.8
onwards, and -mincoming-stack-boundary=3 only from 5.3 onwards. It is
for that reason that an alternative approach (using higher than
necessary alignment) is being used when building with such older
compilers.

Furthermore we should avoid #MF to be raised on the FLDCW we do.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/xen/arch/x86/efi/Makefile b/xen/arch/x86/efi/Makefile
index ad3fdf7ff7e990665eccac826f25e1ae48ed6049..7a743f88881c337447949317908d3cd066de705c 100644 (file)
--- a/xen/arch/x86/efi/Makefile
+++ b/xen/arch/x86/efi/Makefile
@@ -14,5 +14,10 @@ extra-$(efi) += boot.init.o relocs-dummy.o runtime.o compat.o buildid.o
 %.o: %.ihex
        $(OBJCOPY) -I ihex -O binary $< $@
 
+cc-runtime.o := $(CC) -mno-sse
+$(call cc-option-add,cflags-runtime.o,cc-runtime.o,-mpreferred-stack-boundary=3)
+$(call cc-option-add,cflags-runtime.o,cc-runtime.o,-mincoming-stack-boundary=3)
+runtime.o: CFLAGS += $(cflags-runtime.o)
+
 stub.o: $(extra-y)
 nogcov-$(efi) += stub.o

diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index c25681496721f753df29e258967b99a0c1129ffb..926dae69d524693d4bba9a0fedd961eec08131d6 100644 (file)
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -59,12 +59,26 @@ unsigned long efi_rs_enter(void)
     static const u16 fcw = FCW_DEFAULT;
     static const u32 mxcsr = MXCSR_DEFAULT;
     unsigned long cr3 = read_cr3();
+#if __GNUC__ < 5 || (__GNUC__ == 5 && __GNUC_MINOR__ < 3)
+/*
+ * -mpreferred-stack-boundary=3 is can be used only from gcc 4.8 onwards,
+ * and -mincoming-stack-boundary=3 only from 5.3 onwards. Therefore higher
+ * than necessary alignment is being forced here in that case.
+ */
+# define FORCE_ALIGN 32
+#else
+# define FORCE_ALIGN 16
+#endif
+    unsigned long __aligned(FORCE_ALIGN) placeholder[0];
+#undef FORCE_ALIGN
+
+    asm volatile("" : "+m" (placeholder));
 
     if ( !efi_l4_pgtable )
         return 0;
 
     save_fpu_enable();
-    asm volatile ( "fldcw %0" :: "m" (fcw) );
+    asm volatile ( "fnclex; fldcw %0" :: "m" (fcw) );
     asm volatile ( "ldmxcsr %0" :: "m" (mxcsr) );
 
     spin_lock(&efi_rs_lock);