Re: [PATCH for 6.2 38/49] bsd-user: Update mapping to handle reserved and starting conditions

[Richard Henderson <richard.henderson@linaro.org>]

On 8/7/21 11:42 AM, Warner Losh wrote:
> From: Warner Losh <imp@FreeBSD.org>
> 
> Update the reserved base based on what platform we're on, as well as the
> start of the mmap range. Update routines that find va ranges to interact
> with the reserved ranges as well as properly align the mapping (this is
> especially important for targets whose page size does not match the
> host's). Loop where appropriate when the initial address space offered
> by mmap does not meet the contraints.
> 
> Signed-off-by: Mikaël Urankar <mikael.urankar@gmail.com>
> Signed-off-by: Stacey Son <sson@FreeBSD.org>
> Signed-off-by: Warner Losh <imp@bsdimp.com>
> ---
>   bsd-user/main.c |  23 ++-
>   bsd-user/mmap.c | 372 ++++++++++++++++++++++++++++++++++++++++--------
>   bsd-user/qemu.h |   5 +-
>   3 files changed, 335 insertions(+), 65 deletions(-)
> 
> diff --git a/bsd-user/main.c b/bsd-user/main.c
> index 93ef9298b8..36852604f8 100644
> --- a/bsd-user/main.c
> +++ b/bsd-user/main.c
> @@ -49,12 +49,29 @@
>   #include "target_arch_cpu.h"
>   
>   int singlestep;
> -unsigned long mmap_min_addr;
>   uintptr_t guest_base;
>   static const char *cpu_model;
>   static const char *cpu_type;
>   bool have_guest_base;
> +#if (TARGET_LONG_BITS == 32) && (HOST_LONG_BITS == 64)
> +/*
> + * When running 32-on-64 we should make sure we can fit all of the possible
> + * guest address space into a contiguous chunk of virtual host memory.
> + *
> + * This way we will never overlap with our own libraries or binaries or stack
> + * or anything else that QEMU maps.
> + */
> +# ifdef TARGET_MIPS
> +/* MIPS only supports 31 bits of virtual address space for user space */
> +unsigned long reserved_va = 0x77000000;
> +# elif defined(TARGET_PPC64)
> +unsigned long reserved_va = 0xfffff000;
> +# else
> +unsigned long reserved_va = 0xf7000000;
> +# endif
> +#else
>   unsigned long reserved_va;
> +#endif

All of these 7's look to be copying an old linux-user bug.
I cleaned this up in 18e80c55bb6.

Otherwise,
Acked-by: Richard Henderson <richard.henderson@linaro.org>

I would hope one day this memory management could be shared between the user-only 
implementations.  It's complicated enough...


r~