@@ -48,6 +48,7 @@ obj-$(CONFIG_INDIRECT_THUNK) += indirect
obj-$(CONFIG_PV) += ioport_emulate.o
obj-y += irq.o
obj-$(CONFIG_KEXEC) += machine_kexec.o
+obj-y += memcpy.o
obj-y += memset.o
obj-y += mm.o x86_64/mm.o
obj-$(CONFIG_HVM) += monitor.o
@@ -153,12 +153,14 @@ void init_or_livepatch add_nops(void *in
* executing.
*
* "noinline" to cause control flow change and thus invalidate I$ and
- * cause refetch after modification.
+ * cause refetch after modification. While the SDM continues to suggest this
+ * is sufficient, it may not be - issue a serializing insn afterwards as well.
*/
static void init_or_livepatch noinline
text_poke(void *addr, const void *opcode, size_t len)
{
memcpy(addr, opcode, len);
+ cpuid_eax(0);
}
extern void *const __initdata_cf_clobber_start[];
@@ -0,0 +1,20 @@
+#include <asm/asm_defns.h>
+
+FUNC(memcpy)
+ mov %rdx, %rcx
+ mov %rdi, %rax
+ /*
+ * We need to be careful here: memcpy() is involved in alternatives
+ * patching, so the code doing the actual copying (i.e. past setting
+ * up registers) may not be subject to patching (unless further
+ * precautions were taken).
+ */
+ ALTERNATIVE "and $7, %edx; shr $3, %rcx", \
+ "rep movsb; ret", X86_FEATURE_ERMS
+ rep movsq
+ or %edx, %ecx
+ jz 1f
+ rep movsb
+1:
+ ret
+END(memcpy)
@@ -7,21 +7,6 @@
#include <xen/lib.h>
-void *(memcpy)(void *dest, const void *src, size_t n)
-{
- long d0, d1, d2;
-
- asm volatile (
- " rep ; movs"__OS" ; "
- " mov %k4,%k3 ; "
- " rep ; movsb "
- : "=&c" (d0), "=&D" (d1), "=&S" (d2)
- : "0" (n/BYTES_PER_LONG), "r" (n%BYTES_PER_LONG), "1" (dest), "2" (src)
- : "memory" );
-
- return dest;
-}
-
void *(memmove)(void *dest, const void *src, size_t n)
{
long d0, d1, d2;
Move the function to its own assembly file. Having it in C just for the entire body to be an asm() isn't really helpful. Then have two flavors: A "basic" version using qword steps for the bulk of the operation, and an ERMS version for modern hardware, to be substituted in via alternatives patching. Alternatives patching, however, requires an extra precaution: It uses memcpy() itself, and hence the function may patch itself. Luckily the patched-in code only replaces the prolog of the original function. Make sure this remains this way. Additionally alternatives patching, while supposedly safe via enforcing a control flow change when modifying already prefetched code, may not really be. Afaict a request is pending to drop the first of the two options in the SDM's "Handling Self- and Cross-Modifying Code" section. Insert a serializing instruction there. Signed-off-by: Jan Beulich <jbeulich@suse.com> --- We may want to consider branching over the REP MOVSQ as well, if the number of qwords turns out to be zero. We may also want to consider using non-REP MOVS{L,W,B} for the tail. TBD: We may further need a workaround similar to Linux'es 8ca97812c3c8 ("x86/mce: Work around an erratum on fast string copy instructions"). --- v3: Re-base.