hw/i386/microvm: account for SEV c-bit in 64 bit PCI MMIO hole

[PATCH] hw/i386/microvm: account for SEV c-bit in 64 bit PCI MMIO hole

Cyril Leclerc via posted 1 patch 1 day, 17 hours ago

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git fetch https://github.com/patchew-project/qemu tags/patchew/20251216194953.1183260-1-cyril.leclerc@subnoto.com

Maintainers: Sergio Lopez <slp@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Richard Henderson <richard.henderson@linaro.org>, Eduardo Habkost <eduardo@habkost.net>

hw/i386/microvm.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

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[PATCH] hw/i386/microvm: account for SEV c-bit in 64 bit PCI MMIO hole

Posted by Cyril Leclerc via 1 day, 17 hours ago

microvm places the 64-bit PCI MMIO hole at the top of the physical
address space. With SEV, the c-bit reduces the usable address space,
so the MMIO hole ends up at addresses the guest cannot reach (the
guest always strips the c-bit on MMIO accesses).

Fix by placing the MMIO hole within the sev guest addressable range.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3245

Tested-by: Cyril Leclerc <cyril.leclerc@subnoto.com>
Signed-off-by: Cyril Leclerc <cyril.leclerc@subnoto.com>
---
 hw/i386/microvm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
index 94d22a232a..cb43a399ff 100644
--- a/hw/i386/microvm.c
+++ b/hw/i386/microvm.c
@@ -36,6 +36,7 @@
 #include "hw/i386/microvm.h"
 #include "hw/i386/x86.h"
 #include "target/i386/cpu.h"
+#include "target/i386/sev.h"
 #include "hw/intc/i8259.h"
 #include "hw/timer/i8254.h"
 #include "hw/rtc/mc146818rtc.h"
@@ -230,7 +231,11 @@ static void microvm_devices_init(MicrovmMachineState *mms)
 
     if (x86_machine_is_acpi_enabled(x86ms) && mms->pcie == ON_OFF_AUTO_ON) {
         /* use topmost 25% of the address space available */
-        hwaddr phys_size = (hwaddr)1 << X86_CPU(first_cpu)->phys_bits;
+        int phys_bits = X86_CPU(first_cpu)->phys_bits;
+        if (sev_enabled()) {
+            phys_bits -= sev_get_reduced_phys_bits();
+        }
+        hwaddr phys_size = (hwaddr)1 << phys_bits;
         if (phys_size > 0x1000000ll) {
             mms->gpex.mmio64.size = phys_size / 4;
             mms->gpex.mmio64.base = phys_size - mms->gpex.mmio64.size;
-- 
2.47.3