[v4,35/66] kvm/tdx: Ignore memory conversion to shared of unassigned region

Commit Message

Xiaoyao Li Jan. 25, 2024, 3:22 a.m. UTC

From: Isaku Yamahata <[e-mail]>

TDX requires vMMIO region to be shared.  For KVM, MMIO region is the region
which kvm memslot isn't assigned to (except in-kernel emulation).
qemu has the memory region for vMMIO at each device level.

While OVMF issues MapGPA(to-shared) conservatively on 32bit PCI MMIO
region, qemu doesn't find corresponding vMMIO region because it's before
PCI device allocation and memory_region_find() finds the device region, not
PCI bus region.  It's safe to ignore MapGPA(to-shared) because when guest
accesses those region they use GPA with shared bit set for vMMIO.  Ignore
memory conversion request of non-assigned region to shared and return
success.  Otherwise OVMF is confused and panics there.

Signed-off-by: Isaku Yamahata <[e-mail]>
Signed-off-by: Xiaoyao Li <[e-mail]>
---
 accel/kvm/kvm-all.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Patch

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index e26e9121b30d..eb8b3925dbe1 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2943,6 +2943,18 @@  static int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
     section = memory_region_find(get_system_memory(), start, size);
     mr = section.mr;
     if (!mr) {
+        /*
+         * Ignore converting non-assigned region to shared.
+         *
+         * TDX requires vMMIO region to be shared to inject #VE to guest.
+         * OVMF issues conservatively MapGPA(shared) on 32bit PCI MMIO region,
+         * and vIO-APIC 0xFEC00000 4K page.
+         * OVMF assigns 32bit PCI MMIO region to
+         * [top of low memory: typically 2GB=0xC000000,  0xFC00000)
+         */
+        if (!to_private) {
+            return 0;
+        }
         return -1;
     }