[kvm-unit-tests PATCH v3 05/20] x86/virt: Use macro shenanigans to get reg offsets when swapping guest/host regs

[Sean Christopherson <seanjc@google.com>]

Replace the hand-coded literal offsets in the guest/host assembly code
with programmatically generated offsets to make the code more readable and
easier to maintain.  E.g. this will make it much, much easier to make
the guest register structure per-CPU.

To workaround offsetof() being resolved at compile-time, i.e. not by the
preprocessor, provide a macro to define the immediate constraints for
inline assembly.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 lib/x86/virt.h | 62 ++++++++++++++++++++++++++++++++++++--------------
 x86/svm.c      |  5 ++--
 x86/svm.h      | 11 +++++----
 x86/vmx.c      |  3 ++-
 4 files changed, 56 insertions(+), 25 deletions(-)

diff --git a/lib/x86/virt.h b/lib/x86/virt.h
index ccc90c25..1066390d 100644
--- a/lib/x86/virt.h
+++ b/lib/x86/virt.h
@@ -29,24 +29,52 @@ struct guest_regs {
 
 extern struct guest_regs regs;
 
-#define __SWAP_GPRS			\
-	"xchg %%rcx, regs+0x8\n\t"	\
-	"xchg %%rdx, regs+0x10\n\t"	\
-	"xchg %%rbx, regs+0x18\n\t"	\
-	"xchg %%rbp, regs+0x28\n\t"	\
-	"xchg %%rsi, regs+0x30\n\t"	\
-	"xchg %%rdi, regs+0x38\n\t"	\
-	"xchg %%r8, regs+0x40\n\t"	\
-	"xchg %%r9, regs+0x48\n\t"	\
-	"xchg %%r10, regs+0x50\n\t"	\
-	"xchg %%r11, regs+0x58\n\t"	\
-	"xchg %%r12, regs+0x60\n\t"	\
-	"xchg %%r13, regs+0x68\n\t"	\
-	"xchg %%r14, regs+0x70\n\t"	\
-	"xchg %%r15, regs+0x78\n\t"
+#define GUEST_REG_OFFSET(name) \
+	[off_##name] "i" (offsetof(struct guest_regs, name))
 
-#define SWAP_GPRS			\
-	"xchg %%rax, regs+0x0\n\t"	\
+#define GUEST_REGS_OFFSETS	\
+	GUEST_REG_OFFSET(rax),	\
+	GUEST_REG_OFFSET(rcx),	\
+	GUEST_REG_OFFSET(rdx),	\
+	GUEST_REG_OFFSET(rbx),	\
+	GUEST_REG_OFFSET(cr2),	\
+	GUEST_REG_OFFSET(rbp),	\
+	GUEST_REG_OFFSET(rsi),	\
+	GUEST_REG_OFFSET(rdi),	\
+	GUEST_REG_OFFSET(r8),	\
+	GUEST_REG_OFFSET(r9),	\
+	GUEST_REG_OFFSET(r10),	\
+	GUEST_REG_OFFSET(r11),	\
+	GUEST_REG_OFFSET(r12),	\
+	GUEST_REG_OFFSET(r13),	\
+	GUEST_REG_OFFSET(r14),	\
+	GUEST_REG_OFFSET(r15),	\
+	GUEST_REG_OFFSET(rflags)
+
+#define GUEST_REG(name) \
+	xxstr(regs+%c[off_##name])
+
+#define SWAP_REG(name) \
+	"xchg %%" xxstr(name) "," GUEST_REG(name) "\n\t"
+
+#define __SWAP_GPRS		\
+	SWAP_REG(rcx)		\
+	SWAP_REG(rdx)		\
+	SWAP_REG(rbx)		\
+	SWAP_REG(rbp)		\
+	SWAP_REG(rsi)		\
+	SWAP_REG(rdi)		\
+	SWAP_REG(r8)		\
+	SWAP_REG(r9)		\
+	SWAP_REG(r10)		\
+	SWAP_REG(r11)		\
+	SWAP_REG(r12)		\
+	SWAP_REG(r13)		\
+	SWAP_REG(r14)		\
+	SWAP_REG(r15)
+
+#define SWAP_GPRS		\
+	SWAP_REG(rax)		\
 	__SWAP_GPRS
 
 #endif /* _x86_VIRT_H_ */
\ No newline at end of file
diff --git a/x86/svm.c b/x86/svm.c
index 893b3f49..1762cadb 100644
--- a/x86/svm.c
+++ b/x86/svm.c
@@ -254,7 +254,7 @@ u64 __svm_vmrun(u64 rip)
 		      "vmrun %%rax\n\t"               \
 		      ASM_POST_VMRUN_CMD
 		      :
-		      : "a" (virt_to_phys(vmcb))
+		      : GUEST_REGS_OFFSETS, "a" (virt_to_phys(vmcb))
 		      : "memory", "r15");
 
 	return (vmcb->control.exit_code);
@@ -296,7 +296,8 @@ static noinline void test_run(struct svm_test *test)
 			      : // inputs clobbered by the guest:
 				"=D" (the_test),            // first argument register
 				"=b" (the_vmcb)             // callee save register!
-			      : [test] "0" (the_test),
+			      : GUEST_REGS_OFFSETS,
+			        [test] "0" (the_test),
 				[vmcb_phys] "1"(the_vmcb),
 				[PREPARE_GIF_CLEAR] "i" (offsetof(struct svm_test, prepare_gif_clear))
 			      : "rax", "rcx", "rdx", "rsi",
diff --git a/x86/svm.h b/x86/svm.h
index a9e15f67..67a1cddd 100644
--- a/x86/svm.h
+++ b/x86/svm.h
@@ -437,18 +437,18 @@ static inline void clgi(void)
 
 #define ASM_PRE_VMRUN_CMD                       \
                 "vmload %%rax\n\t"              \
-                "mov regs+0x80, %%r15\n\t"      \
+                "mov " GUEST_REG(rflags) ", %%r15\n\t" \
                 "mov %%r15, 0x170(%%rax)\n\t"   \
-                "mov regs, %%r15\n\t"           \
+                "mov " GUEST_REG(rax) ", %%r15\n\t" \
                 "mov %%r15, 0x1f8(%%rax)\n\t"   \
                 __SWAP_GPRS                     \
 
 #define ASM_POST_VMRUN_CMD                      \
                 __SWAP_GPRS                     \
                 "mov 0x170(%%rax), %%r15\n\t"   \
-                "mov %%r15, regs+0x80\n\t"      \
+                "mov %%r15, " GUEST_REG(rflags) "\n\t" \
                 "mov 0x1f8(%%rax), %%r15\n\t"   \
-                "mov %%r15, regs\n\t"           \
+                "mov %%r15, " GUEST_REG(rax)"\n\t" \
                 "vmsave %%rax\n\t"              \
 
 
@@ -459,7 +459,8 @@ static inline void clgi(void)
                 "vmrun %%rax\n\t"               \
 		ASM_POST_VMRUN_CMD \
 		: \
-		: "a" (virt_to_phys(vmcb)) \
+		: GUEST_REGS_OFFSETS, \
+		  "a" (virt_to_phys(vmcb)) \
 		: "memory", "r15") \
 
 #endif
diff --git a/x86/vmx.c b/x86/vmx.c
index 603730c2..8a38ae8a 100644
--- a/x86/vmx.c
+++ b/x86/vmx.c
@@ -1751,7 +1751,8 @@ static noinline void vmx_enter_guest(struct vmentry_result *result)
 		"3: \n\t"
 		: [vm_fail]"+m"(result->vm_fail),
 		  [vm_fail_flags]"=m"(result->flags)
-		: [launched]"m"(launched), [HOST_RSP]"i"(HOST_RSP)
+		: [launched]"m"(launched), [HOST_RSP]"i"(HOST_RSP),
+		  GUEST_REGS_OFFSETS
 		: "rdi", "memory", "cc"
 	);
 	in_guest = 0;
-- 
2.54.0.563.g4f69b47b94-goog