On Thu, Apr 3, 2025 at 2:11 AM Richard Henderson <richard.hender...@linaro.org> wrote: > > On 4/1/25 20:04, Huacai Chen wrote: > > Hi, Richard, > > > > On Tue, Apr 1, 2025 at 9:39 PM Richard Henderson > > <richard.hender...@linaro.org> wrote: > >> > >> On 3/31/25 20:15, Huacai Chen wrote: > >>>> # define TARGET_VIRT_ADDR_SPACE_BITS 32 > >>>> #endif > >>>> #endif > >>>> -#ifdef CONFIG_USER_ONLY > >>>> #define TARGET_PAGE_BITS 12 > >>>> -#else > >>>> -#define TARGET_PAGE_BITS_VARY > >>>> -#define TARGET_PAGE_BITS_MIN 12 > >>>> -#endif > >>> I'm a bit confused about TARGET_PAGE_BITS and other macros. > >>> > >>> In my opinion, if we define TARGET_PAGE_BITS as 12, that means we only > >>> support 4K pages. And if we define TARGET_PAGE_BITS_VARY and > >>> TARGET_PAGE_BITS_MIN as 12, that means we support the minimum page as > >>> 4K, but we also support larger pages. > >>> > >>> Am I wrong? > >> Yes. > >> > >> TARGET_PAGE_BITS is a minimum value that is used by the memory subsystem > >> for managing ram > >> and i/o. If variable, via TARGET_PAGE_BITS_VARY, this is set very early > >> in qemu startup > >> and cannot be changed. > >> > >> The page size for the mips cpu, like many others, may be changed at > >> runtime. The page > >> size used at that point is reported to softmmu during tlb_fill. > >> > >> The value of TARGET_PAGE_BITS must be the minimum supported by the cpu. > >> > >> For Arm, the minimum for armv6 was 1k, then armv7 dropped support for tiny > >> pages so the > >> minimum is 4k. At runtime, armv8 supports page sizes of 4k, 16k, and 64k. > >> > >> For MIPS, ignoring those cpus which support 1k pages, the minimum is 4k. > > If all types of cpus of the target arch has the same minimum supported > > page size, we only need to define TARGET_PAGE_BITS; otherwise we need > > to define TARGET_PAGE_BITS_VARY, and TARGET_PAGE_BITS_MIN means the > > minimum supported page size of the smallest supported page's cpu type. > > Here we remove TARGET_PAGE_BITS_VARY because we just ignore the 1K > > pages. > > > > Am I right now? > > Yes. OK, then it is fine to remove the TARGET_PAGE_BITS_VARY and TARGET_PAGE_BITS_MIN definition. But Loongson still prefers 16K pages (4K pages cause cache alias on Loongson), so I want to keep mc->minimum_page_bits = 14.
Huacai > > > r~
