[v2,23/58] i386/tdx: Make memory type private by default

Commit Message

Xiaoyao Li Aug. 18, 2023, 9:50 a.m. UTC

By default (due to the recent UPM change), restricted memory attribute is
shared.  Convert the memory region from shared to private at the memory
slot creation time.

add kvm region registering function to check the flag
and convert the region, and add memory listener to TDX guest code to set
the flag to the possible memory region.

Without this patch
- Secure-EPT violation on private area
- KVM_MEMORY_FAULT EXIT (kvm -> qemu)
- qemu converts the 4K page from shared to private
- Resume VCPU execution
- Secure-EPT violation again
- KVM resolves EPT Violation
This also prevents huge page because page conversion is done at 4K
granularity.  Although it's possible to merge 4K private mapping into
2M large page, it slows guest boot.

With this patch
- After memory slot creation, convert the region from private to shared
- Secure-EPT violation on private area.
- KVM resolves EPT Violation

Originated-from: Isaku Yamahata <[e-mail]>
Signed-off-by: Xiaoyao Li <[e-mail]>
---
 target/i386/kvm/tdx.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

Patch

diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
index 8a2491ed03c2..775110f8bd02 100644
--- a/target/i386/kvm/tdx.c
+++ b/target/i386/kvm/tdx.c
@@ -18,6 +18,7 @@ 
 #include "standard-headers/asm-x86/kvm_para.h"
 #include "sysemu/kvm.h"
 #include "sysemu/sysemu.h"
+#include "exec/address-spaces.h"
 
 #include "hw/i386/x86.h"
 #include "kvm_i386.h"
@@ -578,6 +579,21 @@  out:
     return r;
 }
 
+static void tdx_guest_region_add(MemoryListener *listener,
+                                 MemoryRegionSection *section)
+{
+    if (memory_region_can_be_private(section->mr)) {
+        memory_region_set_default_private(section->mr);
+    }
+}
+
+static MemoryListener tdx_memory_listener = {
+    .name = TYPE_TDX_GUEST,
+    .region_add = tdx_guest_region_add,
+    /* Higher than KVM memory listener = 10. */
+    .priority = MEMORY_LISTENER_PRIORITY_ACCEL_HIGH,
+};
+
 static bool tdx_guest_get_sept_ve_disable(Object *obj, Error **errp)
 {
     TdxGuest *tdx = TDX_GUEST(obj);
@@ -607,6 +623,12 @@  OBJECT_DEFINE_TYPE_WITH_INTERFACES(TdxGuest,
 static void tdx_guest_init(Object *obj)
 {
     TdxGuest *tdx = TDX_GUEST(obj);
+    static bool memory_listener_registered = false;
+
+    if (!memory_listener_registered) {
+        memory_listener_register(&tdx_memory_listener, &address_space_memory);
+        memory_listener_registered = true;
+    }
 
     qemu_mutex_init(&tdx->lock);