From 8c1e786e506474bae02f81b48a5644afb324d1bb Mon Sep 17 00:00:00 2001
From: Anthony PERARD <anthony.perard@vates.tech>
Date: Mon, 23 Sep 2024 15:59:24 +0200
Subject: OvmfPkg/XenPvBlkDxe: Update disk size calculation

The specification wasn't clear and even contradict itself regarding
the calculation of the disk size. This have been clarified by Xen
commit 221f2748e8da ("blkif: reconcile protocol specification with
in-use implementations").

https://xenbits.xenproject.org/gitweb/?p=xen.git;a=commit;h=221f2748e8dabe8361b8cdfcffbeab9102c4c899

The value from the xenstore node "sectors" must be multiplied by 512
to have the size of the disk.

Calculation of LastBlock is now the same for both CD-ROM case and
generic case.

Signed-off-by: Anthony PERARD <anthony.perard@vates.tech>
---
 OvmfPkg/XenPvBlkDxe/BlockFront.c  |  2 +-
 OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c | 14 +++++++++-----
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/OvmfPkg/XenPvBlkDxe/BlockFront.c b/OvmfPkg/XenPvBlkDxe/BlockFront.c
index 5a3ad5e4e5..eb503eb7c1 100644
--- a/OvmfPkg/XenPvBlkDxe/BlockFront.c
+++ b/OvmfPkg/XenPvBlkDxe/BlockFront.c
@@ -356,7 +356,7 @@ Again:
 
   DEBUG ((
     DEBUG_INFO,
-    "XenPvBlk: New disk with %ld sectors of %d bytes\n",
+    "XenPvBlk: New disk with %ld 512B-sectors and logical sector size of %d bytes\n",
     Dev->MediaInfo.Sectors,
     Dev->MediaInfo.SectorSize
     ));
diff --git a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
index dfc40bffaa..218ada89c6 100644
--- a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
+++ b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
@@ -295,15 +295,19 @@ XenPvBlkDxeDriverBindingStart (
     //    MdeModulePkg/Universal/Disk/PartitionDxe/ElTorito.c
     //
     Media->BlockSize = 2048;
-    Media->LastBlock = DivU64x32 (
-                         Dev->MediaInfo.Sectors,
-                         Media->BlockSize / Dev->MediaInfo.SectorSize
-                         ) - 1;
   } else {
     Media->BlockSize = Dev->MediaInfo.SectorSize;
-    Media->LastBlock = Dev->MediaInfo.Sectors - 1;
   }
 
+  //
+  // Sectors is express as 512B unit, size of disk is "Sectors * 512",
+  // independently from SectorSize.
+  //
+  Media->LastBlock = DivU64x32 (
+                       Dev->MediaInfo.Sectors,
+                       Media->BlockSize / 512
+                       ) - 1;
+
   ASSERT (Media->BlockSize % 512 == 0);
   Dev->BlockIo.Media = Media;
 
-- 
cgit