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[PATCH v4 2/2] drivers/char: Use sub-page ro API to make just xhci dbc cap RO



Not the whole page, which may contain other registers too. The XHCI
specification describes DbC as designed to be controlled by a different
driver, but does not mandate placing registers on a separate page. In fact
on Tiger Lake and newer (at least), this page do contain other registers
that Linux tries to use. And with share=yes, a domU would use them too.
Without this patch, PV dom0 would fail to initialize the controller,
while HVM would be killed on EPT violation.

With `share=yes`, this patch gives domU more access to the emulator
(although a HVM with any emulated device already has plenty of it). This
configuration is already documented as unsafe with untrusted guests and
not security supported.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
Changes in v4:
- restore mmio_ro_ranges in the fallback case
- set XHCI_SHARE_NONE in the fallback case
Changes in v3:
- indentation fix
- remove stale comment
- fallback to pci_ro_device() if subpage_mmio_ro_add() fails
- extend commit message
Changes in v2:
 - adjust for simplified subpage_mmio_ro_add() API
---
 xen/drivers/char/xhci-dbc.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/xen/drivers/char/xhci-dbc.c b/xen/drivers/char/xhci-dbc.c
index 8e2037f1a5f7..c45e4b6825cc 100644
--- a/xen/drivers/char/xhci-dbc.c
+++ b/xen/drivers/char/xhci-dbc.c
@@ -1216,20 +1216,28 @@ static void __init cf_check 
dbc_uart_init_postirq(struct serial_port *port)
         break;
     }
 #ifdef CONFIG_X86
-    /*
-     * This marks the whole page as R/O, which may include other registers
-     * unrelated to DbC. Xen needs only DbC area protected, but it seems
-     * Linux's XHCI driver (as of 5.18) works without writting to the whole
-     * page, so keep it simple.
-     */
-    if ( rangeset_add_range(mmio_ro_ranges,
-                PFN_DOWN((uart->dbc.bar_val & PCI_BASE_ADDRESS_MEM_MASK) +
-                         uart->dbc.xhc_dbc_offset),
-                PFN_UP((uart->dbc.bar_val & PCI_BASE_ADDRESS_MEM_MASK) +
-                       uart->dbc.xhc_dbc_offset +
-                sizeof(*uart->dbc.dbc_reg)) - 1) )
-        printk(XENLOG_INFO
-               "Error while adding MMIO range of device to mmio_ro_ranges\n");
+    if ( subpage_mmio_ro_add(
+             (uart->dbc.bar_val & PCI_BASE_ADDRESS_MEM_MASK) +
+              uart->dbc.xhc_dbc_offset,
+             sizeof(*uart->dbc.dbc_reg)) )
+    {
+        printk(XENLOG_WARNING
+               "Error while marking MMIO range of XHCI console as R/O, "
+               "making the whole device R/O (share=no)\n");
+        uart->dbc.share = XHCI_SHARE_NONE;
+        if ( pci_ro_device(0, uart->dbc.sbdf.bus, uart->dbc.sbdf.devfn) )
+            printk(XENLOG_WARNING
+                   "Failed to mark read-only %pp used for XHCI console\n",
+                   &uart->dbc.sbdf);
+        if ( rangeset_add_range(mmio_ro_ranges,
+                 PFN_DOWN((uart->dbc.bar_val & PCI_BASE_ADDRESS_MEM_MASK) +
+                          uart->dbc.xhc_dbc_offset),
+                 PFN_UP((uart->dbc.bar_val & PCI_BASE_ADDRESS_MEM_MASK) +
+                        uart->dbc.xhc_dbc_offset +
+                        sizeof(*uart->dbc.dbc_reg)) - 1) )
+            printk(XENLOG_INFO
+                   "Error while adding MMIO range of device to 
mmio_ro_ranges\n");
+    }
 #endif
 }
 
-- 
git-series 0.9.1



 


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