Re: [kvm-unit-tests PATCH v4 4/6] s390x: Add library functions for exiting from snippet

["Nico Boehr" <nrb@xxxxxxxxxxxxx>]

On Wed Oct 16, 2024 at 8:03 PM CEST, Nina Schoetterl-Glausch wrote:
> It is useful to be able to force an exit to the host from the snippet,
> as well as do so while returning a value.
> Add this functionality, also add helper functions for the host to check
> for an exit and get or check the value.
> Use diag 0x44 and 0x9c for this.
> Add a guest specific snippet header file and rename snippet.h to reflect
> that it is host specific.
>
> Signed-off-by: Nina Schoetterl-Glausch <nsg@xxxxxxxxxxxxx>

Hi Nina,

would you mind if I fix this up like this?

(copy-pasted so whitespace damage ahead)

diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
index 2dec7924..03adcd3c 100644
--- a/lib/s390x/asm/arch_def.h
+++ b/lib/s390x/asm/arch_def.h
@@ -510,11 +510,14 @@ static inline void diag44(void)
 	asm volatile("diag	0,0,0x44\n");
 }

-static inline void diag9c(uint64_t val)
+static inline void diag500(uint64_t val)
 {
-	asm volatile("diag	%[val],0,0x9c\n"
+	asm volatile(
+		"lgr	2,%[val]\n"
+		"diag	0,0,0x500\n"
 		:
 		: [val] "d"(val)
+		: "r2"
 	);
 }

diff --git a/lib/s390x/snippet-exit.h b/lib/s390x/snippet-exit.h
index f62f0068..3ed4c22c 100644
--- a/lib/s390x/snippet-exit.h
+++ b/lib/s390x/snippet-exit.h
@@ -19,16 +19,14 @@ static inline bool snippet_is_force_exit(struct vm *vm)

 static inline bool snippet_is_force_exit_value(struct vm *vm)
 {
-	return sie_is_diag_icpt(vm, 0x9c);
+	return sie_is_diag_icpt(vm, 0x500);
 }

 static inline uint64_t snippet_get_force_exit_value(struct vm *vm)
 {
-	struct kvm_s390_sie_block *sblk = vm->sblk;
-
 	assert(snippet_is_force_exit_value(vm));

-	return vm->save_area.guest.grs[sblk_ip_as_diag(sblk).r_1];
+	return vm->save_area.guest.grs[2];
 }

 static inline void snippet_check_force_exit_value(struct vm *vm, uint64_t value_exp)
diff --git a/s390x/snippets/lib/snippet-exit.h b/s390x/snippets/lib/snippet-exit.h
index 0b483366..ac00de3f 100644
--- a/s390x/snippets/lib/snippet-exit.h
+++ b/s390x/snippets/lib/snippet-exit.h
@@ -21,7 +21,7 @@ static inline void force_exit(void)
 static inline void force_exit_value(uint64_t val)
 {
 	mb(); /* host may read any memory written by the guest before */
-	diag9c(val);
+	diag500(val);
 	mb(); /* allow host to modify guest memory */
 }