virtio-mem: Default to "unplugged-inaccessible=on" with 8.1 on x86-64

Allowing guests to read unplugged memory simplified the bring-up of
virtio-mem in Linux guests -- which was limited to x86-64 only. On arm64
(which was added later), we never had legacy guests and don't even allow
to configure it, essentially always having "unplugged-inaccessible=on".

At this point, all guests we care about
should be supporting VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, so let's
change the default for the 8.1 machine.

This change implies that also memory that supports the shared zeropage
(private anonymous memory) will now require
VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE in the driver in order to be usable by
the guest -- as default, one can still manually set the
unplugged-inaccessible property.

Disallowing the guest to read unplugged memory will be important for
some future features, such as memslot optimizations or protection of
unplugged memory, whereby we'll actually no longer allow the guest to
even read from unplugged memory.

At some point, we might want to deprecate and remove that property.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Eduardo Habkost <eduardo@habkost.net>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230503182352.792458-1-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index d761c8c7753e456729611eac9bf6623015733e5f..7802dc21d92890c91f3b5290102a5885e0640d08 100644 (file)
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -116,7 +116,9 @@
     { "qemu64-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },\
     { "athlon-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },
 
-GlobalProperty pc_compat_8_0[] = {};
+GlobalProperty pc_compat_8_0[] = {
+    { "virtio-mem", "unplugged-inaccessible", "auto" },
+};
 const size_t pc_compat_8_0_len = G_N_ELEMENTS(pc_compat_8_0);
 
 GlobalProperty pc_compat_7_2[] = {

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 957fe77dc002a949320b270320916f62f59ccc29..538b695c29de495d7dd09d425bfcff05a65368ae 100644 (file)
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -1341,7 +1341,7 @@ static Property virtio_mem_properties[] = {
                      TYPE_MEMORY_BACKEND, HostMemoryBackend *),
 #if defined(VIRTIO_MEM_HAS_LEGACY_GUESTS)
     DEFINE_PROP_ON_OFF_AUTO(VIRTIO_MEM_UNPLUGGED_INACCESSIBLE_PROP, VirtIOMEM,
-                            unplugged_inaccessible, ON_OFF_AUTO_AUTO),
+                            unplugged_inaccessible, ON_OFF_AUTO_ON),
 #endif
     DEFINE_PROP_BOOL(VIRTIO_MEM_EARLY_MIGRATION_PROP, VirtIOMEM,
                      early_migration, true),