[PATCH v3 4/7] vpci: fix updating the command register

[Roger Pau Monne <roger.pau@citrix.com>]

When switching the memory decoding bit in the command register the
rest of the changes where dropped, leading to only the memory decoding
bit being updated.

Fix this by unconditionally writing the guest-requested command except
for the memory decoding bit, which will be updated once the p2m
changes are performed.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <julien.grall@arm.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Wei Liu <wei.liu2@citrix.com>
---
 xen/drivers/vpci/header.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index 0ec4c082a6..9234de9b26 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -333,8 +333,10 @@ static void cmd_write(const struct pci_dev *pdev, unsigned int reg,
          * hoping the guest will realize and try again.
          */
         modify_bars(pdev, cmd & PCI_COMMAND_MEMORY, false);
-    else
-        pci_conf_write16(pdev->seg, pdev->bus, slot, func, reg, cmd);
+
+    /* Write the new command without updating the memory decoding bit. */
+    cmd = (cmd & ~PCI_COMMAND_MEMORY) | (current_cmd & PCI_COMMAND_MEMORY);
+    pci_conf_write16(pdev->seg, pdev->bus, slot, func, reg, cmd);
 }
 
 static void bar_write(const struct pci_dev *pdev, unsigned int reg,
-- 
2.19.1


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