Re: [PATCH v6 2/3] xen/arm32: Create the same boot-time MPU regions as arm64

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 14/04/2025 13:12, Ayan Kumar Halder wrote:
> Hi Michal,
> 
> On 14/04/2025 09:38, Orzel, Michal wrote:
>>
>> On 11/04/2025 13:04, Ayan Kumar Halder wrote:
>>> Boot-time MPU protection regions (similar to Armv8-R AArch64) are created 
>>> for
>>> Armv8-R AArch32.
>>> Also, defined *_PRBAR macros for arm32. The only difference from arm64 is 
>>> that
>>> XN is 1-bit for arm32.
>>> Defined the system registers and macros in mpu/cpregs.h.
>>>
>>> Introduced WRITE_SYSREG_ASM() to write to system registers in assembly.
>> It really reads odd when you write what patch does in past tense.
> I will change it.
>>
>>> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
>>> Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
>>> ---
>>> Changes from
>>>
>>> v1 -
>>>
>>> 1. enable_mpu() now sets HMAIR{0,1} registers. This is similar to what is
>>> being done in enable_mmu(). All the mm related configurations happen in this
>>> function.
>>>
>>> 2. Fixed some typos.
>>>
>>> v2 -
>>> 1. Include the common prepare_xen_region.inc in head.S.
>>>
>>> 2. Define LOAD_SYSREG()/STORE_SYSREG() for arm32.
>>>
>>> v3 -
>>> 1. Rename STORE_SYSREG() as WRITE_SYSREG_ASM()
>>>
>>> 2. enable_boot_cpu_mm() is defined in head.S
>>>
>>> v4 -
>>> 1. *_PRBAR is moved to arm32/sysregs.h.
>>>
>>> 2. MPU specific CP15 system registers are defined in mpu/cpregs.h.
>>>
>>> v5 -
>>> 1. WRITE_SYSREG_ASM is enclosed within #ifdef __ASSEMBLY__
>>>
>>> 2. enable_mpu() clobbers r0 only.
>>>
>>> 3. Definitions in mpu/cpregs.h in enclosed within ARM_32.
>>>
>>> 4. Removed some #ifdefs and style changes.
>>>
>>>   xen/arch/arm/arm32/Makefile              |   1 +
>>>   xen/arch/arm/arm32/mpu/Makefile          |   1 +
>>>   xen/arch/arm/arm32/mpu/head.S            | 104 +++++++++++++++++++++++
>>>   xen/arch/arm/include/asm/arm32/sysregs.h |   9 ++
>>>   xen/arch/arm/include/asm/cpregs.h        |   2 +
>>>   xen/arch/arm/include/asm/mpu/cpregs.h    |  27 ++++++
>>>   6 files changed, 144 insertions(+)
>>>   create mode 100644 xen/arch/arm/arm32/mpu/Makefile
>>>   create mode 100644 xen/arch/arm/arm32/mpu/head.S
>>>   create mode 100644 xen/arch/arm/include/asm/mpu/cpregs.h
>>>
>>> diff --git a/xen/arch/arm/arm32/Makefile b/xen/arch/arm/arm32/Makefile
>>> index 40a2b4803f..537969d753 100644
>>> --- a/xen/arch/arm/arm32/Makefile
>>> +++ b/xen/arch/arm/arm32/Makefile
>>> @@ -1,5 +1,6 @@
>>>   obj-y += lib/
>>>   obj-$(CONFIG_MMU) += mmu/
>>> +obj-$(CONFIG_MPU) += mpu/
>>>   
>>>   obj-$(CONFIG_EARLY_PRINTK) += debug.o
>>>   obj-y += domctl.o
>>> diff --git a/xen/arch/arm/arm32/mpu/Makefile 
>>> b/xen/arch/arm/arm32/mpu/Makefile
>>> new file mode 100644
>>> index 0000000000..3340058c08
>>> --- /dev/null
>>> +++ b/xen/arch/arm/arm32/mpu/Makefile
>>> @@ -0,0 +1 @@
>>> +obj-y += head.o
>>> diff --git a/xen/arch/arm/arm32/mpu/head.S b/xen/arch/arm/arm32/mpu/head.S
>>> new file mode 100644
>>> index 0000000000..b2c5245e51
>>> --- /dev/null
>>> +++ b/xen/arch/arm/arm32/mpu/head.S
>>> @@ -0,0 +1,104 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +/*
>>> + * Start-of-day code for an Armv8-R-AArch32 MPU system.
>>> + */
>>> +
>>> +#include <asm/arm32/macros.h>
>>> +#include <asm/arm32/sysregs.h>
>>> +#include <asm/cpregs.h>
>>> +#include <asm/mpu.h>
>>> +#include <asm/mpu/regions.inc>
>>> +#include <asm/page.h>
>>> +
>>> +/*
>>> + * Set up the memory attribute type tables and enable EL2 MPU and data 
>>> cache.
>>> + * If the Background region is enabled, then the MPU uses the default 
>>> memory
>>> + * map as the Background region for generating the memory
>>> + * attributes when MPU is disabled.
>>> + * Since the default memory map of the Armv8-R AArch32 architecture is
>>> + * IMPLEMENTATION DEFINED, we intend to turn off the Background region 
>>> here.
>>> + *
>>> + * Clobbers r0
>>> + */
>>> +FUNC_LOCAL(enable_mpu)
>>> +    /* Set up memory attribute type tables */
>>> +    mov_w r0, MAIR0VAL
>>> +    mcr   CP32(r0, HMAIR0)
>>> +    mov_w r0, MAIR1VAL
>>> +    mcr   CP32(r0, HMAIR1)
>>> +
>>> +    mrc   CP32(r0, HSCTLR)
>>> +    bic   r0, r0, #SCTLR_ELx_BR       /* Disable Background region */
>>> +    orr   r0, r0, #SCTLR_Axx_ELx_M    /* Enable MPU */
>>> +    orr   r0, r0, #SCTLR_Axx_ELx_C    /* Enable D-cache */
>>> +    mcr   CP32(r0, HSCTLR)
>>> +    isb
>>> +
>>> +    ret
>>> +END(enable_mpu)
>>> +
>>> +/*
>>> + * Maps the various sections of Xen (described in xen.lds.S) as different 
>>> MPU
>>> + * regions.
>>> + *
>>> + * Clobbers r0 - r5
>>> + *
>>> + */
>>> +FUNC(enable_boot_cpu_mm)
>>> +    /* Get the number of regions specified in MPUIR_EL2 */
>>> +    mrc   CP32(r5, MPUIR_EL2)
>>> +    and   r5, r5, #NUM_MPU_REGIONS_MASK
>>> +
>>> +    /* x0: region sel */
>>> +    mov   r0, #0
>>> +    /* Xen text section. */
>>> +    mov_w   r1, _stext
>>> +    mov_w   r2, _etext
>>> +    prepare_xen_region r0, r1, r2, r3, r4, r5, attr_prbar=REGION_TEXT_PRBAR
>>> +
>>> +    /* Xen read-only data section. */
>>> +    mov_w   r1, _srodata
>>> +    mov_w   r2, _erodata
>>> +    prepare_xen_region r0, r1, r2, r3, r4, r5, attr_prbar=REGION_RO_PRBAR
>>> +
>>> +    /* Xen read-only after init and data section. (RW data) */
>>> +    mov_w   r1, __ro_after_init_start
>>> +    mov_w   r2, __init_begin
>>> +    prepare_xen_region r0, r1, r2, r3, r4, r5
>>> +
>>> +    /* Xen code section. */
>>> +    mov_w   r1, __init_begin
>>> +    mov_w   r2, __init_data_begin
>>> +    prepare_xen_region r0, r1, r2, r3, r4, r5, attr_prbar=REGION_TEXT_PRBAR
>>> +
>>> +    /* Xen data and BSS section. */
>>> +    mov_w   r1, __init_data_begin
>>> +    mov_w   r2, __bss_end
>>> +    prepare_xen_region r0, r1, r2, r3, r4, r5
>>> +
>>> +#ifdef CONFIG_EARLY_PRINTK
>>> +    /* Xen early UART section. */
>>> +    mov_w   r1, CONFIG_EARLY_UART_BASE_ADDRESS
>>> +    mov_w   r2, (CONFIG_EARLY_UART_BASE_ADDRESS + CONFIG_EARLY_UART_SIZE)
>>> +    prepare_xen_region r0, r1, r2, r3, r4, r5, 
>>> attr_prbar=REGION_DEVICE_PRBAR, attr_prlar=REGION_DEVICE_PRLAR
>>> +#endif
>>> +
>>> +    b    enable_mpu
>>> +END(enable_boot_cpu_mm)
>>> +
>>> +/*
>>> + * We don't yet support secondary CPUs bring-up. Implement a dummy helper 
>>> to
>>> + * please the common code.
>>> + */
>>> +FUNC(enable_secondary_cpu_mm)
>>> +    PRINT("- SMP not enabled yet -\r\n")
>>> +1:  wfe
>>> +    b 1b
>>> +END(enable_secondary_cpu_mm)
>>> +
>>> +/*
>>> + * Local variables:
>>> + * mode: ASM
>>> + * indent-tabs-mode: nil
>>> + * End:
>>> + */
>>> diff --git a/xen/arch/arm/include/asm/arm32/sysregs.h 
>>> b/xen/arch/arm/include/asm/arm32/sysregs.h
>>> index 22871999af..8d7b95d982 100644
>>> --- a/xen/arch/arm/include/asm/arm32/sysregs.h
>>> +++ b/xen/arch/arm/include/asm/arm32/sysregs.h
>>> @@ -20,6 +20,15 @@
>>>    * uses r0 as a placeholder register. */
>>>   #define CMD_CP32(name...)      "mcr " __stringify(CP32(r0, name)) ";"
>>>   
>>> +#define REGION_TEXT_PRBAR       0x18    /* SH=11 AP=10 XN=0 */
>>> +#define REGION_RO_PRBAR         0x1D    /* SH=11 AP=10 XN=1 */
>>> +#define REGION_DATA_PRBAR       0x19    /* SH=11 AP=00 XN=1 */
>>> +#define REGION_DEVICE_PRBAR     0x11    /* SH=10 AP=00 XN=1 */
>>> +
>>> +#ifdef __ASSEMBLY__
>> In previous patch, you had empty lines surrounding the macro.
> I will put a empty line here.
>>
>>> +#define WRITE_SYSREG_ASM(v, name) mcr CP32(v, name)
>> Hmm, for arm64 you surrounded msr within "". Any reason for these style 
>> changes?
> 
> In arm64, it is
> 
> "msr " __stringify(name,) #v
> 
> One needs " " to treat this as string for concatenation. Otherwise, we 
> get an error.
> 
> In the case of arm32, we don't need __stringify().
> 
> Let me know if it makes sense.
It does. Thanks for providing the reasoning.

~Michal