[PATCH] passthru: Fix pci bar remapping for passthru devices

[Wei Wang2 <wei.wang2@amd.com>]

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Hi, 
When guest code tries to get the block size of mmio, it will write all "1"s 
into pci bar register and then qemu will return all "0"s to the don't care 
bits in the emulated bar register to indicate the block size to guest code. 
In this case, we should not create p2m mapping in  pt_bar_reg_write() and
pt_exp_rom_bar_reg_write(). Attached patch fixes this issue, additional 
comment can be found in the patch.

Thanks,
Wei

Signed-off-by: Wei Wang <wei.wang2@amd.com>
--
 AMD GmbH, Germany
 Operating System Research Center
 
 Legal Information:
 Advanced Micro Devices GmbH
 Karl-Hammerschmidt-Str. 34
 85609 Dornach b. München
 
 Geschäftsführer: Jochen Polster, Thomas M. McCoy, Giuliano Meroni
 Sitz: Dornach, Gemeinde Aschheim, Landkreis München
 Registergericht München, HRB Nr. 43632

[-- Attachment #2: mmio.patch --]
[-- Type: text/x-diff, Size: 1710 bytes --]

diff --git a/hw/pass-through.c b/hw/pass-through.c
index 51a39db..009b902 100644
--- a/hw/pass-through.c
+++ b/hw/pass-through.c
@@ -3177,7 +3177,16 @@ static int pt_bar_reg_write(struct pt_dev *ptdev,
     }
 
     /* update the corresponding virtual region address */
-    r->addr = cfg_entry->data;
+    /*
+     * When guest code tries to get block size of mmio, it will write all "1"s
+     * into pci bar register. In this case, cfg_entry->data == writable_mask.
+     * Especially for devices with large mmio, the value of writable_mask
+     * is likely to be a guest physical address that has been mapped to ram
+     * rather than mmio. Remapping this value to mmio should be prevented.
+     */
+
+    if ( cfg_entry->data != writable_mask )
+        r->addr = cfg_entry->data;
 
 exit:
     /* create value for writing to I/O device register */
@@ -3229,7 +3238,16 @@ static int pt_exp_rom_bar_reg_write(struct pt_dev *ptdev,
     cfg_entry->data = PT_MERGE_VALUE(*value, cfg_entry->data, writable_mask);
 
     /* update the corresponding virtual region address */
-    r->addr = cfg_entry->data;
+    /*
+     * When guest code tries to get block size of mmio, it will write all "1"s
+     * into pci bar register. In this case, cfg_entry->data == writable_mask.
+     * Especially for devices with large mmio, the value of writable_mask
+     * is likely to be a guest physical address that has been mapped to ram
+     * rather than mmio. Remapping this value to mmio should be prevented.
+     */
+
+    if ( cfg_entry->data != writable_mask )
+        r->addr = cfg_entry->data;
 
     /* create value for writing to I/O device register */
     throughable_mask = ~bar_emu_mask & valid_mask;

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