[Xen-changelog] [xen master] x86/EFI: meet further spec requirements for runtime calls

[patchbot@xxxxxxx]

commit 67b5b302f5319f70288587dc98ab505c4deada1e
Author:     Jan Beulich <JBeulich@xxxxxxxx>
AuthorDate: Thu Nov 10 09:06:30 2016 -0700
Commit:     Wei Liu <wei.liu2@xxxxxxxxxx>
CommitDate: Sat Nov 12 06:47:10 2016 +0000

    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@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
    Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 xen/arch/x86/efi/Makefile |  5 +++++
 xen/common/efi/runtime.c  | 16 +++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/efi/Makefile b/xen/arch/x86/efi/Makefile
index ad3fdf7..7a743f8 100644
--- 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 c256814..926dae6 100644
--- 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);
--
generated by git-patchbot for /home/xen/git/xen.git#master

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