[PATCH v2 01/19] accel/kvm: Add helper for handling conversions of MMIO holes

[Michael Roth <michael.roth@amd.com>]

When converting GPA ranges containing MMIO holes, the general intended
logic is to skip MMIO ranges as long as it is a private->shared
conversion, and to fail otherwise.

To better enable some future refactorings to address bugs in the current
code, go ahead and consolidate all of the MMIO handling to a
self-contained helper.

The only intended functional change is that the error message for
shared->private conversion of MMIO ranges corresponding to a
non-RAM/non-ROM region now report the range of the region that
specifically caused the failure, as opposed to reporting the entire
conversion range.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c | 96 ++++++++++++++++++++++++++++++---------------
 1 file changed, 64 insertions(+), 32 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 70605a8d10..0b59ba0d3c 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3334,6 +3334,67 @@ static void kvm_eat_signals(CPUState *cpu)
     } while (sigismember(&chkset, SIG_IPI));
 }
 
+/*
+ * This handles checking whether a conversion overlaps with any holes in
+ * the given section/range, and indicates whether or not the section/range
+ * can be safely skipped (which is generally allowed as long as the
+ * conversion is private->shared and not the other way around).
+ *
+ * Returns 0 if section is normal guest-memfd-backed memory, or is a hole or
+ * non-RAM/ROM region that should be skipped as MMIO. In the latter case, the
+ * 'skip' parameter will be set. Returns < 0 if the conversion request is not
+ * valid.
+ */
+static int handle_memory_hole(MemoryRegionSection *section, bool to_private,
+                              bool *skip)
+{
+    MemoryRegion *mr = section->mr;
+
+    if (!mr) {
+        /*
+         * 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 the current lookup failed to find any regions, then skip the
+         * entire remaining range as a hole/MMIO.
+         */
+        if (!to_private) {
+            *skip = true;
+            return 0;
+        }
+        return -EINVAL;
+    }
+
+    /*
+     * Because vMMIO region must be shared, guest TD may convert vMMIO
+     * region to shared explicitly.  Don't complain such case.  See
+     * memory_region_type() for checking if the region is MMIO region.
+     */
+    if (!memory_region_has_guest_memfd_private(mr)) {
+        if (!to_private &&
+            !memory_region_is_ram(mr) &&
+            !memory_region_is_ram_device(mr) &&
+            !memory_region_is_rom(mr) &&
+            !memory_region_is_romd(mr)) {
+            *skip = true;
+            return 0;
+        } else {
+            error_report("Convert non guest_memfd backed memory region "
+                         "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s",
+                         section->offset_within_address_space,
+                         int128_get64(section->size),
+                         to_private ? "private" : "shared");
+            return -EINVAL;
+        }
+    }
+
+    *skip = false;
+    return 0;
+}
+
 int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
 {
     MemoryRegionSection section;
@@ -3341,6 +3402,7 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
     MemoryRegion *mr;
     RAMBlock *rb;
     void *addr;
+    bool skip;
     int ret = -EINVAL;
 
     trace_kvm_convert_memory(start, size, to_private ? "shared_to_private" : "private_to_shared");
@@ -3356,39 +3418,9 @@ 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 ret;
-    }
 
-    if (!memory_region_has_guest_memfd_private(mr)) {
-        /*
-         * Because vMMIO region must be shared, guest TD may convert vMMIO
-         * region to shared explicitly.  Don't complain such case.  See
-         * memory_region_type() for checking if the region is MMIO region.
-         */
-        if (!to_private &&
-            !memory_region_is_ram(mr) &&
-            !memory_region_is_ram_device(mr) &&
-            !memory_region_is_rom(mr) &&
-            !memory_region_is_romd(mr)) {
-            ret = 0;
-        } else {
-            error_report("Convert non guest_memfd backed memory region "
-                        "(0x%"HWADDR_PRIx" ,+ 0x%"HWADDR_PRIx") to %s",
-                        start, size, to_private ? "private" : "shared");
-        }
+    ret = handle_memory_hole(&section, to_private, &skip);
+    if (ret || skip) {
         goto out_unref;
     }
 
-- 
2.43.0