[Devel] [PATCH hci-8.1 v5 5/5] selftests/ve: check CPUID override emulation for a prefixed CPUID

[Konstantin Khorenko <khorenko@virtuozzo.com>]

Execute CPUID with an operand-size prefix, which the CPU ignores, and
expect the table values. Before the kernel change the #GP handler
matched only the bare opcode and the child died with SIGSEGV.

https://virtuozzo.atlassian.net/browse/VSTOR-148843

Feature: x86: cpu pools (cpuid override)
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 .../testing/selftests/ve/ve_cpuid_override_test.c  | 32 +++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/ve/ve_cpuid_override_test.c b/tools/testing/selftests/ve/ve_cpuid_override_test.c
index f944fb5d806f6..98649d7df8ed4 100644
--- a/tools/testing/selftests/ve/ve_cpuid_override_test.c
+++ b/tools/testing/selftests/ve/ve_cpuid_override_test.c
@@ -47,6 +47,17 @@ static void do_cpuid(unsigned int leaf, struct cpuid_regs *r)
 	__cpuid_count(leaf, 0, r->eax, r->ebx, r->ecx, r->edx);
 }
 
+/* CPUID with an operand-size prefix, which the CPU accepts and ignores. */
+static void do_cpuid_prefixed(unsigned int leaf, struct cpuid_regs *r)
+{
+	/* ebx is the PIC base on i386; swap it out like <cpuid.h> does. */
+	asm volatile("xchg %%ebx, %1\n\t"
+		     ".byte 0x66, 0x0f, 0xa2\n\t"
+		     "xchg %%ebx, %1"
+		     : "=a" (r->eax), "=&r" (r->ebx), "=c" (r->ecx), "=d" (r->edx)
+		     : "a" (leaf), "c" (0));
+}
+
 /* Voluntary context switches of a task, from its /proc status file. */
 static int read_nvcsw(const char *status, unsigned long *nvcsw)
 {
@@ -63,6 +74,7 @@ static int read_nvcsw(const char *status, unsigned long *nvcsw)
 struct child_ctx {
 	int result_pipe[2];
 	int stop;
+	int prefixed;
 };
 
 /*
@@ -92,7 +104,10 @@ static int cpuid_child(struct child_ctx *ctx)
 			return 24;
 	}
 
-	do_cpuid(CPUID_LEAF, &r);
+	if (ctx->prefixed)
+		do_cpuid_prefixed(CPUID_LEAF, &r);
+	else
+		do_cpuid(CPUID_LEAF, &r);
 
 	if (write(ctx->result_pipe[1], &r, sizeof(r)) != sizeof(r))
 		return 25;
@@ -324,4 +339,19 @@ TEST_F(ve_cpuid_override, armed_before_first_reschedule)
 	}
 }
 
+TEST_F(ve_cpuid_override, prefixed_cpuid_is_emulated)
+{
+	struct child_ctx ctx = { .stop = 1, .prefixed = 1 };
+	struct cpuid_regs r;
+	pid_t pid;
+
+	ASSERT_EQ(write_file_at(AT_FDCWD, CPUID_OVERRIDE_PATH, self->table), 0);
+
+	pid = spawn_cpuid_child(_metadata, self, &ctx);
+	resume_cpuid_child(_metadata, pid);
+	collect_cpuid_child(_metadata, self, &ctx, &r);
+
+	EXPECT_EQ(r.edx, self->host.edx & ~self->bit);
+}
+
 TEST_HARNESS_MAIN

-- 
2.43.0

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