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/x86_64/xen_shinfo_test.c b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
index d2ea0435f4f7..1ba06551526b 100644
--- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
@@ -171,8 +171,9 @@ static volatile bool guest_saw_irq;
 static void evtchn_handler(struct ex_regs *regs)
 {
 	struct vcpu_info *vi = (void *)VCPU_INFO_VADDR;
-	vi->evtchn_upcall_pending = 0;
-	vi->evtchn_pending_sel = 0;
+
+	vcpu_arch_put_guest(vi->evtchn_upcall_pending, 0);
+	vcpu_arch_put_guest(vi->evtchn_pending_sel, 0);
 	guest_saw_irq = true;
 
 	GUEST_SYNC(TEST_GUEST_SAW_IRQ);