Why rtems arm bsp do not set xn flag when config mmu device region?

[tianye]

Hi:

Why rtems arm bsp do not set xn flag when config mmu device region?

#define AARCH64_MMU_FLAGS_BASE \

  ( MMU_DESC_VALID | MMU_DESC_SH_INNER | MMU_DESC_AF )

#define AARCH64_MMU_DATA_RO_CACHED \

  ( AARCH64_MMU_FLAGS_BASE | MMU_DESC_MAIR_ATTR( 3 ) | MMU_DESC_WRITE_DISABLE )

#define AARCH64_MMU_CODE_CACHED AARCH64_MMU_DATA_RO_CACHED

#define AARCH64_MMU_CODE_RW_CACHED AARCH64_MMU_DATA_RW_CACHED

#define AARCH64_MMU_DATA_RO \

  ( AARCH64_MMU_FLAGS_BASE | MMU_DESC_MAIR_ATTR( 1 ) | MMU_DESC_WRITE_DISABLE )

#define AARCH64_MMU_CODE AARCH64_MMU_DATA_RO

#define AARCH64_MMU_CODE_RW AARCH64_MMU_DATA_RW

/* RW implied by not ORing in RO */

#define AARCH64_MMU_DATA_RW_CACHED \

  ( AARCH64_MMU_FLAGS_BASE | MMU_DESC_MAIR_ATTR( 3 ) )

#define AARCH64_MMU_DATA_RW \

  ( AARCH64_MMU_FLAGS_BASE | MMU_DESC_MAIR_ATTR( 1 ) )

#define AARCH64_MMU_DEVICE ( AARCH64_MMU_FLAGS_BASE | MMU_DESC_MAIR_ATTR( 0 ) )

ARM datasheet(ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition):

Any region of memory that is read-sensitive must be marked as Execute Never, 

to avoid the possibility of a speculative prefetch accessing the memory region. 

For example, any memory region that corresponds to a read-sensitive peripheral 

must be marked as Execute Never.

and linux mmu config:

 #define PROT_DEVICE_nGnRnE  (PROT_DEFAULT | PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE | PTE_ATTRINDX(MT_DEVICE_nGnRnE))

 #define PROT_DEVICE_nGnRE   (PROT_DEFAULT | PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE | PTE_ATTRINDX(MT_DEVICE_nGnRE))

 #define PROT_NORMAL_NC      (PROT_DEFAULT | PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE | PTE_ATTRINDX(MT_NORMAL_NC))

 #define PROT_NORMAL_WT      (PROT_DEFAULT | PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE | PTE_ATTRINDX(MT_NORMAL_WT))

 #define PROT_NORMAL     (PROT_DEFAULT | PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE | PTE_ATTRINDX(MT_NORMAL))

 #define PROT_SECT_DEVICE_nGnRE  (PROT_SECT_DEFAULT | PMD_SECT_PXN | PMD_SECT_UXN | PMD_ATTRINDX(MT_DEVICE_nGnRE))

 #define PROT_SECT_NORMAL    (PROT_SECT_DEFAULT | PMD_SECT_PXN | PMD_SECT_UXN | PMD_ATTRINDX(MT_NORMAL))

 #define PROT_SECT_NORMAL_EXEC   (PROT_SECT_DEFAULT | PMD_SECT_UXN | PMD_ATTRINDX(MT_NORMAL))

 #define _PAGE_DEFAULT       (_PROT_DEFAULT | PTE_ATTRINDX(MT_NORMAL))

 #define _HYP_PAGE_DEFAULT   _PAGE_DEFAULT

 #define PAGE_KERNEL     __pgprot(PROT_NORMAL)

 #define PAGE_KERNEL_RO      __pgprot((PROT_NORMAL & ~PTE_WRITE) | PTE_RDONLY)

 #define PAGE_KERNEL_ROX     __pgprot((PROT_NORMAL & ~(PTE_WRITE | PTE_PXN)) | PTE_RDONLY)

 #define PAGE_KERNEL_EXEC    __pgprot(PROT_NORMAL & ~PTE_PXN)

 #define PAGE_KERNEL_EXEC_CONT   __pgprot((PROT_NORMAL & ~PTE_PXN) | PTE_CONT)

Thanks!

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