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riscv: add RISC-V Svpbmt extension support
Svpbmt (the S should be capitalized) is the "Supervisor-mode: page-based memory types" extension that specifies attributes for cacheability, idempotency and ordering. The relevant settings are done in special bits in PTEs: Here is the svpbmt PTE format: | 63 | 62-61 | 60-8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 N MT RSW D A G U X W R V ^ Of the Reserved bits [63:54] in a leaf PTE, the high bit is already allocated (as the N bit), so bits [62:61] are used as the MT (aka MemType) field. This field specifies one of three memory types that are close equivalents (or equivalent in effect) to the three main x86 and ARMv8 memory types - as shown in the following table. RISC-V Encoding & MemType RISC-V Description ---------- ------------------------------------------------ 00 - PMA Normal Cacheable, No change to implied PMA memory type 01 - NC Non-cacheable, idempotent, weakly-ordered Main Memory 10 - IO Non-cacheable, non-idempotent, strongly-ordered I/O memory 11 - Rsvd Reserved for future standard use As the extension will not be present on all implementations use alternatives to check its existence at runtime and if needed adapt the code to use memory-types. Signed-off-by: Wei Fu <wefu@redhat.com> Co-developed-by: Liu Shaohua <liush@allwinnertech.com> Signed-off-by: Liu Shaohua <liush@allwinnertech.com> Co-developed-by: Guo Ren <guoren@kernel.org> Signed-off-by: Guo Ren <guoren@kernel.org> [moved to use the alternatives mechanism] Co-developed-by: Heiko Stuebner <heiko@sntech.de> Signed-off-by: Heiko Stuebner <heiko@sntech.de>
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