KVM: selftests: Add coverage for 'b' (byte) sized fastops emulation

Extend the fastops test to cover instructions that operate on 8-bit data.
Support for 8-bit instructions was omitted from the original commit purely
due to complications with BT not having a r/m8 variant.  To keep the
RFLAGS.CF behavior deterministic and not heavily biased to '0' or '1',
continue using BT, but cast and load the to-be-tested value into a
dedicated 32-bit constraint.

Supporting 8-bit operations will allow using guest_test_fastops() as-is to
provide full coverage for DIV and IDIV.  For divide operations, covering
all operand sizes _is_ interesting, because KVM needs provide exception
fixup for each size (failure to handle a #DE could panic the host).

Link: https://lore.kernel.org/all/aIF7ZhWZxlkcpm4y@google.com
Link: https://lore.kernel.org/r/20250909202835.333554-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/x86/fastops_test.c b/tools/testing/selftests/kvm/x86/fastops_test.c
index 2ac89d6c1e468a0b14f6e62985ac43072ac632e7..6c9a2dbf63657ed7e74b41dce1d3a3609c90be1c 100644 (file)
--- a/tools/testing/selftests/kvm/x86/fastops_test.c
+++ b/tools/testing/selftests/kvm/x86/fastops_test.c
@@ -10,12 +10,13 @@
  */
 #define guest_execute_fastop_1(FEP, insn, __val, __flags)                              \
 ({                                                                                     \
-       __asm__ __volatile__("bt $0, %[val]\n\t"                                        \
+       __asm__ __volatile__("bt $0, %[ro_val]\n\t"                                     \
                             FEP insn " %[val]\n\t"                                     \
                             "pushfq\n\t"                                               \
                             "pop %[flags]\n\t"                                         \
                             : [val]"+r"(__val), [flags]"=r"(__flags)                   \
-                            : : "cc", "memory");                                       \
+                            : [ro_val]"rm"((uint32_t)__val)                            \
+                            : "cc", "memory");                                         \
 })
 
 #define guest_test_fastop_1(insn, type_t, __val)                                       \
@@ -36,12 +37,13 @@
 
 #define guest_execute_fastop_2(FEP, insn, __input, __output, __flags)                  \
 ({                                                                                     \
-       __asm__ __volatile__("bt $0, %[output]\n\t"                                     \
+       __asm__ __volatile__("bt $0, %[ro_val]\n\t"                                     \
                             FEP insn " %[input], %[output]\n\t"                        \
                             "pushfq\n\t"                                               \
                             "pop %[flags]\n\t"                                         \
                             : [output]"+r"(__output), [flags]"=r"(__flags)             \
-                            : [input]"r"(__input) : "cc", "memory");                   \
+                            : [input]"r"(__input), [ro_val]"rm"((uint32_t)__output)    \
+                            : "cc", "memory");                                         \
 })
 
 #define guest_test_fastop_2(insn, type_t, __val1, __val2)                              \
@@ -63,12 +65,13 @@
 
 #define guest_execute_fastop_cl(FEP, insn, __shift, __output, __flags)                 \
 ({                                                                                     \
-       __asm__ __volatile__("bt $0, %[output]\n\t"                                     \
+       __asm__ __volatile__("bt $0, %[ro_val]\n\t"                                     \
                             FEP insn " %%cl, %[output]\n\t"                            \
                             "pushfq\n\t"                                               \
                             "pop %[flags]\n\t"                                         \
                             : [output]"+r"(__output), [flags]"=r"(__flags)             \
-                            : "c"(__shift) : "cc", "memory");                          \
+                            : "c"(__shift), [ro_val]"rm"((uint32_t)__output)           \
+                            : "cc", "memory");                                         \
 })
 
 #define guest_test_fastop_cl(insn, type_t, __val1, __val2)                             \
@@ -115,14 +118,16 @@ do {                                                                                      \
                        guest_test_fastop_2("add" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("adc" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("and" suffix, type_t, vals[i], vals[j]);    \
+if (sizeof(type_t) != 1) {                                                     \
                        guest_test_fastop_2("bsf" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("bsr" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("bt" suffix, type_t, vals[i], vals[j]);     \
                        guest_test_fastop_2("btc" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("btr" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("bts" suffix, type_t, vals[i], vals[j]);    \
-                       guest_test_fastop_2("cmp" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("imul" suffix, type_t, vals[i], vals[j]);   \
+}                                                                                      \
+                       guest_test_fastop_2("cmp" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("or" suffix, type_t, vals[i], vals[j]);     \
                        guest_test_fastop_2("sbb" suffix, type_t, vals[i], vals[j]);    \
                        guest_test_fastop_2("sub" suffix, type_t, vals[i], vals[j]);    \
@@ -142,6 +147,7 @@ do {                                                                                        \
 
 static void guest_code(void)
 {
+       guest_test_fastops(uint8_t, "b");
        guest_test_fastops(uint16_t, "w");
        guest_test_fastops(uint32_t, "l");
        guest_test_fastops(uint64_t, "q");