KVM: selftests: Add vcpu_arch_put_guest() to do writes from guest code

Introduce a macro, vcpu_arch_put_guest(), for "putting" values to memory
from guest code in "interesting" situations, e.g. when writing memory that
is being dirty logged.  Structure the macro so that arch code can provide
a custom implementation, e.g. x86 will use the macro to force emulation of
the access.

Use the helper in dirty_log_test, which is of particular interest (see
above), and in xen_shinfo_test, which isn't all that interesting, but
provides a second usage of the macro with a different size operand
(uint8_t versus uint64_t), i.e. to help verify that the macro works for
more than just 64-bit values.

Use "put" as the verb to align with the kernel's {get,put}_user()
terminology.

Link: https://lore.kernel.org/r/20240314185459.2439072-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index aaf6d61c08db..a83cbc7b7f0d 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -105,7 +105,7 @@ static void guest_code(void)
 	 */
 	for (i = 0; i < guest_num_pages; i++) {
 		addr = guest_test_virt_mem + i * guest_page_size;
-		*(uint64_t *)addr = READ_ONCE(iteration);
+		vcpu_arch_put_guest(*(uint64_t *)addr, READ_ONCE(iteration));
 	}
 
 	while (true) {
@@ -114,7 +114,8 @@ static void guest_code(void)
 			addr += (guest_random_u64(&guest_rng) % guest_num_pages)
 				* guest_page_size;
 			addr = align_down(addr, host_page_size);
-			*(uint64_t *)addr = READ_ONCE(iteration);
+
+			vcpu_arch_put_guest(*(uint64_t *)addr, READ_ONCE(iteration));
 		}
 
 		GUEST_SYNC(1);