On 8/5/23 19:58, Richard Henderson wrote:
On 8/5/23 10:43, Helge Deller wrote:
If there were a way to change no more than two lines of code,
that would be fine. But otherwise I don't see this as being
worth making the rest of the code base any more complex.
Ok. What about that 6-line patch below for x86? It's trivial and
all what's needed for x86. Btw, any index which is >= 9 will use
the shorter code sequence.
Helge
diff --git a/target/i386/cpu.h b/target/i386/cpu.h index
e0771a1043..3e71e666db 100644 --- a/target/i386/cpu.h +++
b/target/i386/cpu.h @@ -2251,11 +2251,11 @@ uint64_t
cpu_get_tsc(CPUX86State *env); #define cpu_list x86_cpu_list
/* MMU modes definitions */ -#define MMU_KSMAP_IDX 0 -#define
MMU_USER_IDX 1 -#define MMU_KNOSMAP_IDX 2 -#define
MMU_NESTED_IDX 3 -#define MMU_PHYS_IDX 4 +#define MMU_KSMAP_IDX
11 +#define MMU_USER_IDX 12 +#define MMU_KNOSMAP_IDX 13 +#define
MMU_NESTED_IDX 14 +#define MMU_PHYS_IDX 15
No. The small patch would need to apply to all guests.
Yes.
Perhaps something to handle indexing of CPUTLBDescFast, e.g.
static inline CPUTLBDescFast cputlb_fast(CPUTLB *tlb, unsigned idx)
{ return &tlb->f[NB_MMU_MODES - 1 - idx]; }
There's already tlb_mask_table_ofs, which handles all tcg backends;
you just need to adjust that and cputlb.c> Introduce cputlb_fast with
normal indexing in one patch, and then the second patch to invert the
indexing may well be exactly two lines. :-)
You're cheating :-)
But ok, that's an easy one and I can come up with both patches.
One last idea which came into my mind and which may be worth
asking before I start to hack the patch above...:
include/exec/cpu-defs.h:
/* add some comment here why we use this transformation: */
#define MMU_INDEX(nr) (NB_MMU_MODES - 1 - (x))
target/*/cpu.h:
/* MMU modes definitions */
#define MMU_KSMAP_IDX MMU_INDEX(0)
#define MMU_USER_IDX MMU_INDEX(1)
#define MMU_KNOSMAP_IDX MMU_INDEX(2)
#define MMU_NESTED_IDX MMU_INDEX(3)
...
Downside:
- of course it's a lot more than the 2 lines you asked for
Upsides:
- no additional subtaction at tcg compile time/runtime
- clear indication that this is an MMU index, easy to grep.
- easy to use
?
Helge
