Re: [PATCH for 4-21 v4] xen/riscv: identify specific ISA supported by cpu

[Oleksii Kurochko]

On 2/7/25 5:47 PM, Oleksii Kurochko wrote:

On 2/4/25 12:47 PM, Jan Beulich wrote:

+const struct riscv_isa_ext_data __initconst riscv_isa_ext[] = {
+    RISCV_ISA_EXT_DATA(i, RISCV_ISA_EXT_i),
+    RISCV_ISA_EXT_DATA(m, RISCV_ISA_EXT_m),
+    RISCV_ISA_EXT_DATA(a, RISCV_ISA_EXT_a),
+    RISCV_ISA_EXT_DATA(f, RISCV_ISA_EXT_f),
+    RISCV_ISA_EXT_DATA(d, RISCV_ISA_EXT_d),
+    RISCV_ISA_EXT_DATA(q, RISCV_ISA_EXT_q),
+    RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
+    RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
+    RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
+    RISCV_ISA_EXT_DATA(zifencei, RISCV_ISA_EXT_ZIFENCEI),
+    RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
+    RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
+    RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
+    RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
+    RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
+};
+
+static const struct riscv_isa_ext_data __initconst required_extensions[] = {
+    RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
+    RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
+    RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
+};

Coming back to my earlier question regarding the B (pseudo-)extension:
Since riscv_isa_ext[] only contains Zbb, is it precluded anywhere in
the spec that DT may mention just B when all of its constituents are
supported?

Which gets me on to G, which is somewhat similar in nature to B. We
require G when RISCV_ISA_RV64G=y, yet required_extensions[] doesn't
name it or its constituents. Much like we require C when RISCV_ISA_C=y,
yet it's not in the table.

Another one thing I am thinking about if we really need a separate 
required_extensions[] array.

We can leave only riscv_isa_ext[] and then just do a check:
  bitmap_weight(riscv_isa, ...) == ARRAY_SIZE(riscv_isa_ext)

It seems like we still need to have two arrays: one for what Xen is supported 
(and could be passed to guest
by riscv,isa) and one for what is required for boot.

~ Oleksii