[PATCH v3 6/6] i386/pc: restrict AMD only enforcing of valid IOVAs to new machine type

[Joao Martins <joao.m.martins@oracle.com>]

The added enforcing is only relevant in the case of AMD where the
range right before the 1TB is restricted and cannot be DMA mapped
by the kernel consequently leading to IOMMU INVALID_DEVICE_REQUEST
or possibly other kinds of IOMMU events in the AMD IOMMU.

Although, there's a case where it may make sense to disable the
IOVA relocation/validation when migrating from a
non-valid-IOVA-aware qemu to one that supports it.

Relocating RAM regions to after the 1Tb hole has consequences for
guest ABI because we are changing the memory mapping, so make
sure that only new machine enforce but not older ones.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 hw/i386/pc.c         | 6 ++++++
 hw/i386/pc_piix.c    | 2 ++
 hw/i386/pc_q35.c     | 2 ++
 include/hw/i386/pc.h | 1 +
 4 files changed, 11 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 11598a0a39e4..ef0a5325f98a 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -859,9 +859,14 @@ static hwaddr x86_max_phys_addr(PCMachineState *pcms,
 static void x86_update_above_4g_mem_start(PCMachineState *pcms,
                                           uint64_t pci_hole64_size)
 {
+    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
     X86MachineState *x86ms = X86_MACHINE(pcms);
     uint32_t eax, vendor[3];
 
+    if (!pcmc->enforce_valid_iova) {
+        return;
+    }
+
     host_cpuid(0x0, 0, &eax, &vendor[0], &vendor[2], &vendor[1]);
     if (!IS_AMD_VENDOR(vendor)) {
         return;
@@ -1804,6 +1809,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     pcmc->has_reserved_memory = true;
     pcmc->kvmclock_enabled = true;
     pcmc->enforce_aligned_dimm = true;
+    pcmc->enforce_valid_iova = true;
     /* BIOS ACPI tables: 128K. Other BIOS datastructures: less than 4K reported
      * to be used at the moment, 32K should be enough for a while.  */
     pcmc->acpi_data_size = 0x20000 + 0x8000;
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 5a608e30e28f..c322f9494384 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -435,9 +435,11 @@ DEFINE_I440FX_MACHINE(v7_0, "pc-i440fx-7.0", NULL,
 
 static void pc_i440fx_6_2_machine_options(MachineClass *m)
 {
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
     pc_i440fx_7_0_machine_options(m);
     m->alias = NULL;
     m->is_default = false;
+    pcmc->enforce_valid_iova = false;
     compat_props_add(m->compat_props, hw_compat_6_2, hw_compat_6_2_len);
     compat_props_add(m->compat_props, pc_compat_6_2, pc_compat_6_2_len);
 }
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index c81d21d1ebb4..53ed6df1e0e0 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -379,8 +379,10 @@ DEFINE_Q35_MACHINE(v7_0, "pc-q35-7.0", NULL,
 
 static void pc_q35_6_2_machine_options(MachineClass *m)
 {
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
     pc_q35_7_0_machine_options(m);
     m->alias = NULL;
+    pcmc->enforce_valid_iova = false;
     compat_props_add(m->compat_props, hw_compat_6_2, hw_compat_6_2_len);
     compat_props_add(m->compat_props, pc_compat_6_2, pc_compat_6_2_len);
 }
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index d8b9c4ebd748..914340750498 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -117,6 +117,7 @@ struct PCMachineClass {
     bool has_reserved_memory;
     bool enforce_aligned_dimm;
     bool broken_reserved_end;
+    bool enforce_valid_iova;
 
     /* generate legacy CPU hotplug AML */
     bool legacy_cpu_hotplug;
-- 
2.17.2