[PATCH v1 1/2] xen/mpu: Map early uart when earlyprintk on

[Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>]

CONFIG_EARLY_UART_SIZE is introduced to let user provide physical size of
early UART. Unlike MMU where we map a page in the virtual address space,
here we need to know the exact physical size to be mapped.
As VA == PA in case of MPU, the memory layout follows exactly the hardware
configuration. As a consequence, we set  EARLY_UART_VIRTUAL_ADDRESS as physical
address.

Further, we check whether user-defined EARLY_UART_SIZE is aligned to PAGE_SIZE
(4KB). This is partly because we intend to map a minimum of 1 page(ie 4KB) and
the limit address is set as "EARLY_UART_SIZE-1". The limit address needs to end
with 0x3f (as required by PRLAR register).

UART is mapped as nGnRE region (as specified by ATTR=100 , refer G1.3.13,
MAIR_EL2, "---0100 Device memory nGnRE") and Doc ID - 102670_0101_02_en
Table 4-3, Armv8 architecture memory types (nGnRE - Corresponds to Device in
Armv7 architecture). Also, it is mapped as outer shareable, RW at EL2 only
and execution of instructions from the region is not permitted.

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
---
 xen/arch/arm/Kconfig.debug              |  7 +++++++
 xen/arch/arm/arm64/mpu/head.S           |  9 +++++++++
 xen/arch/arm/include/asm/early_printk.h | 19 +++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/xen/arch/arm/Kconfig.debug b/xen/arch/arm/Kconfig.debug
index 7660e599c0..84a0616102 100644
--- a/xen/arch/arm/Kconfig.debug
+++ b/xen/arch/arm/Kconfig.debug
@@ -121,6 +121,13 @@ config EARLY_UART_BASE_ADDRESS
        hex "Early printk, physical base address of debug UART"
        range 0x0 0xffffffff if ARM_32
 
+config EARLY_UART_SIZE
+       depends on EARLY_PRINTK
+       depends on MPU
+       hex "Early printk, physical size of debug UART"
+       range 0x0 0xffffffff if ARM_32
+       default 0x1000
+
 config EARLY_UART_PL011_BAUD_RATE
        depends on EARLY_UART_PL011
        int "Early printk UART baud rate for pl011"
diff --git a/xen/arch/arm/arm64/mpu/head.S b/xen/arch/arm/arm64/mpu/head.S
index 731698aa3b..98422d7ed3 100644
--- a/xen/arch/arm/arm64/mpu/head.S
+++ b/xen/arch/arm/arm64/mpu/head.S
@@ -11,8 +11,10 @@
 #define REGION_TEXT_PRBAR       0x38    /* SH=11 AP=10 XN=00 */
 #define REGION_RO_PRBAR         0x3A    /* SH=11 AP=10 XN=10 */
 #define REGION_DATA_PRBAR       0x32    /* SH=11 AP=00 XN=10 */
+#define REGION_DEVICE_PRBAR     0x22    /* SH=10 AP=00 XN=10 */
 
 #define REGION_NORMAL_PRLAR     0x0f    /* NS=0 ATTR=111 EN=1 */
+#define REGION_DEVICE_PRLAR     0x09    /* NS=0 ATTR=100 EN=1 */
 
 /*
  * Macro to prepare and set a EL2 MPU memory region.
@@ -137,6 +139,13 @@ FUNC(enable_boot_cpu_mm)
     ldr   x2, =__bss_end
     prepare_xen_region x0, x1, x2, x3, x4, x5
 
+#ifdef CONFIG_EARLY_PRINTK
+    /* Xen early UART section. */
+    ldr   x1, =CONFIG_EARLY_UART_BASE_ADDRESS
+    ldr   x2, =(CONFIG_EARLY_UART_BASE_ADDRESS + CONFIG_EARLY_UART_SIZE)
+    prepare_xen_region x0, x1, x2, x3, x4, x5, attr_prbar=REGION_DEVICE_PRBAR, 
attr_prlar=REGION_DEVICE_PRLAR
+#endif
+
     b    enable_mpu
     ret
 END(enable_boot_cpu_mm)
diff --git a/xen/arch/arm/include/asm/early_printk.h 
b/xen/arch/arm/include/asm/early_printk.h
index 46a5e562dd..98fd52c4db 100644
--- a/xen/arch/arm/include/asm/early_printk.h
+++ b/xen/arch/arm/include/asm/early_printk.h
@@ -15,6 +15,24 @@
 
 #ifdef CONFIG_EARLY_PRINTK
 
+#ifndef CONFIG_MMU
+
+/*
+ * For MPU systems, there is no VMSA support in EL2, so we use VA == PA
+ * for EARLY_UART_VIRTUAL_ADDRESS.
+ */
+#define EARLY_UART_VIRTUAL_ADDRESS CONFIG_EARLY_UART_BASE_ADDRESS
+
+/*
+ * User-defined EARLY_UART_SIZE must be aligned to a PAGE_SIZE, or
+ * we may map more than necessary in MPU system.
+ */
+#if (EARLY_UART_SIZE % PAGE_SIZE) != 0
+#error "EARLY_UART_SIZE must be aligned to PAGE_SIZE"
+#endif
+
+#else
+
 /* need to add the uart address offset in page to the fixmap address */
 #define EARLY_UART_VIRTUAL_ADDRESS \
     (FIXMAP_ADDR(FIX_CONSOLE) + (CONFIG_EARLY_UART_BASE_ADDRESS & ~PAGE_MASK))
@@ -22,6 +40,7 @@
 #define TEMPORARY_EARLY_UART_VIRTUAL_ADDRESS \
     (TEMPORARY_FIXMAP_ADDR(FIX_CONSOLE) + (CONFIG_EARLY_UART_BASE_ADDRESS & 
~PAGE_MASK))
 
+#endif /* CONFIG_MMU */
 #endif /* !CONFIG_EARLY_PRINTK */
 
 #endif
-- 
2.25.1