[PATCH] drivers/char: mark XHCI DMA buffers reserved in memory map

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

The IOMMU driver checks if RMRR/IVMD are marked as reserved in memory
map. This should be true for addresses coming from the firmware, but
when extra pages used by Xen itself are included in the mapping, those
are taken from usable RAM used. Mark those pages as reserved too.

Not marking the pages as reserved didn't caused issues before due to
another a bug in IOMMU driver code, that was fixed in 83afa3135830
("amd-vi: fix IVMD memory type checks").

Failing to reserve memory will lead to panic in IOMMU setup code. And
not including the page in IOMMU mapping will lead to broken console (on
due to IOMMU faults). Handling failure with panic() isn't the most user
friendly thing, but at this stage the alternative would require undoing
a lot of console init. Since the user can do it much easier - by simply
not enabling xhci console next time, say that and panic.

Fixes: 3a1a7b809ffa "drivers/char: mark DMA buffers as reserved for the XHCI"
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
As an alternative implementation I have considered changing
iommu_get_extra_reserved_device_memory() to modify memory map. But that
may hide (or cause) some other issues when this API will gain some more
users in the future.

The reserve_e820_ram() is x86-specific. Is there some equivalent API for
ARM, or maybe even some abstract one? That said, I have no way to test
XHCI console on ARM, I don't know if such hardware even exists...
---
 xen/arch/x86/setup.c        |  3 +++
 xen/drivers/char/xhci-dbc.c | 22 ++++++++++++++++++++++
 xen/include/xen/serial.h    |  2 ++
 3 files changed, 27 insertions(+)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index a21984b1ccd8..8ab89b3710ed 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1806,6 +1806,9 @@ void asmlinkage __init noreturn __start_xen(unsigned long 
mbi_p)
     mmio_ro_ranges = rangeset_new(NULL, "r/o mmio ranges",
                                   RANGESETF_prettyprint_hex);
 
+    /* Needs to happen after E820 processing but before IOMMU init */
+    xhci_dbc_uart_reserve_ram();
+
     xsm_multiboot_init(module_map, mbi);
 
     /*
diff --git a/xen/drivers/char/xhci-dbc.c b/xen/drivers/char/xhci-dbc.c
index 3bf389be7d0b..e31f3cba7838 100644
--- a/xen/drivers/char/xhci-dbc.c
+++ b/xen/drivers/char/xhci-dbc.c
@@ -31,6 +31,9 @@
 #include <asm/io.h>
 #include <asm/string.h>
 #include <asm/system.h>
+#ifdef CONFIG_X86
+#include <asm/e820.h>
+#endif
 
 /* uncomment to have dbc_uart_dump() debug function */
 /* #define DBC_DEBUG 1 */
@@ -1426,6 +1429,25 @@ void __init xhci_dbc_uart_init(void)
     }
 }
 
+void __init xhci_dbc_uart_reserve_ram(void)
+{
+    struct dbc *dbc = &dbc_uart.dbc;
+
+    if ( !dbc->enable )
+        return;
+
+#ifdef CONFIG_X86
+    if ( !reserve_e820_ram(
+            &e820,
+            virt_to_maddr(&dbc_dma_bufs),
+            virt_to_maddr(&dbc_dma_bufs) + sizeof(dbc_dma_bufs) - 1) )
+        panic("Failed to reserve XHCI DMA buffers (%"PRIx64"-%"PRIx64"), "
+              "disable xhci console to work around\n",
+              virt_to_maddr(&dbc_dma_bufs),
+              virt_to_maddr(&dbc_dma_bufs) + sizeof(dbc_dma_bufs) - 1);
+#endif
+}
+
 #ifdef DBC_DEBUG
 static void dbc_dump(struct dbc *dbc)
 {
diff --git a/xen/include/xen/serial.h b/xen/include/xen/serial.h
index 3d21207a3d7a..bb48eb8e8bd9 100644
--- a/xen/include/xen/serial.h
+++ b/xen/include/xen/serial.h
@@ -162,8 +162,10 @@ void ns16550_init(int index, struct ns16550_defaults 
*defaults);
 void ehci_dbgp_init(void);
 #ifdef CONFIG_XHCI
 void xhci_dbc_uart_init(void);
+void xhci_dbc_uart_reserve_ram(void);
 #else
 static void inline xhci_dbc_uart_init(void) {}
+static void inline xhci_dbc_uart_reserve_ram(void) {}
 #endif
 
 void arm_uart_init(void);
-- 
2.43.0