Linux panic if the VGA region isn't reserved.

When Linux is booted on EFI system, it expects the memory at 0xa0000 to
_not_ be conventional memory. Otherwise a variable isn't initialised
properly and Linux panic when a virtual console/terminal is asked to be
created.

See for more detail:
https://lists.xenproject.org/archives/html/xen-devel/2019-03/msg02139.html

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1689
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
---

Notes:
    v3:
    - fix commit message

 OvmfPkg/XenPlatformPei/Xen.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/OvmfPkg/XenPlatformPei/Xen.c b/OvmfPkg/XenPlatformPei/Xen.c
index 62a2c3ed93..9866b7c212 100644
--- a/OvmfPkg/XenPlatformPei/Xen.c
+++ b/OvmfPkg/XenPlatformPei/Xen.c
@@ -291,6 +291,12 @@ XenPublishRamRegions (
   Status = XenGetE820Map (&E820Map, &E820EntriesCount);
   ASSERT_EFI_ERROR (Status);
 
+  AddMemoryBaseSizeHob (0, 0xA0000);
+  //
+  // Video memory + Legacy BIOS region, to allow Linux to boot.
+  //
+  AddReservedMemoryBaseSizeHob (0xA0000, BASE_1MB - 0xA0000, TRUE);
+
   for (Index = 0; Index < E820EntriesCount; Index++) {
     UINT64 Base;
     UINT64 End;
@@ -304,6 +310,16 @@ XenPublishRamRegions (
     Base = ALIGN_VALUE (Entry->BaseAddr, (UINT64)EFI_PAGE_SIZE);
     End = (Entry->BaseAddr + Entry->Length) & ~(UINT64)EFI_PAGE_MASK;
 
+    //
+    // Ignore the first 1MB, this is handled before the loop.
+    //
+    if (Base < BASE_1MB) {
+      Base = BASE_1MB;
+    }
+    if (Base >= End) {
+      continue;
+    }
+
     switch (Entry->Type) {
     case EfiAcpiAddressRangeMemory:
       AddMemoryRangeHob (Base, End);
-- 
Anthony PERARD


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