[PATCH v3 37/70] kvm/tdx: Ignore memory conversion to shared of unassigned region

Xiaoyao Li
2023-11-15T07:20:12Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

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 <isaku.yamahata@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
accel/kvm/kvm-all.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 5e862db4af41..89e7183a2738 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2942,6 +2942,18 @@ 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) {
+ ret = 0;
+ }
return ret;
}

--
2.34.1