[PATCH 2/2] arm64: mm: support bootparam max_addr

[Peng Fan]

> Subject: Re: [PATCH 2/2] arm64: mm: support bootparam max_addr
> 
> On Wed, 15 Dec 2021 at 07:56, Peng Fan (OSS) <peng.fan at oss.nxp.com>
> wrote:
> >
> > From: Peng Fan <peng.fan at nxp.com>
> >
> > There is a "mem=[x]" boot parameter, but when there is a whole
> > reserved by secure TEE, the continuous DRAM area is split with two
> memblocks.
> >
> > For example, DRAM area [0x40000000, 0xffffffff], when TEE uses
> > [0x50000000, 0x51000000), the memblock will be split into [0x40000000,
> > 0x50000000) and [0x51000000, 0xffffffff].
> >
> > If pass "mem=1024MB", the actually max addr will be 0x81000000.
> > However if need the max addr be 0x80000000, mem=1008MB should be
> used.
> >
> > There also might be multiple other holes that no visible to Linux,
> > when we wanna to limit the max addr usable by Linux, using
> > "max_addr=[X]" is much easier than "mem=[X]"
> >
> > Signed-off-by: Peng Fan <peng.fan at nxp.com>
> 
> mem= is a hack already, please don't add another one. Limiting the memory
> like this is far too tricky, given that the kernel itself and the initrd could end up
> in memory that is excluded, and we have to go and fix things up if that
> happens.

We wanna to use the reserved memory with request_mem_region, but with
commit 86588296acbfb1 ("fdt: Properly handle "no-map" field in the memory region ")

request_mem_region will fail, because the reserved memory are now as
kernel memory.

So we use "mem=X" to work around the issue, but "mem=X" is not user friendly
compared with "max_addr=" when there are multiple holes used by others.

Thanks,
Peng.

> 
> 
> > ---
> >  arch/arm64/mm/init.c | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> >
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index
> > db63cc885771..3364b5e7a7fe 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -173,6 +173,7 @@ int pfn_is_map_memory(unsigned long pfn)
> > EXPORT_SYMBOL(pfn_is_map_memory);
> >
> >  static phys_addr_t memory_limit __ro_after_init = PHYS_ADDR_MAX;
> > +static phys_addr_t max_addr __ro_after_init = PHYS_ADDR_MAX;
> >
> >  /*
> >   * Limit the memory size that was specified via FDT.
> > @@ -189,6 +190,18 @@ static int __init early_mem(char *p)  }
> > early_param("mem", early_mem);
> >
> > +static int __init set_max_addr(char *p) {
> > +       if (!p)
> > +               return 1;
> > +
> > +       max_addr = memparse(p, &p) & PAGE_MASK;
> > +       pr_notice("Memory max addr set to 0x%llx\n", max_addr);
> > +
> > +       return 0;
> > +}
> > +early_param("max_addr", set_max_addr);
> > +
> >  void __init arm64_memblock_init(void)  {
> >         s64 linear_region_size = PAGE_END -
> > _PAGE_OFFSET(vabits_actual); @@ -253,6 +266,9 @@ void __init
> arm64_memblock_init(void)
> >                 memblock_add(__pa_symbol(_text), (u64)(_end -
> _text));
> >         }
> >
> > +       if (max_addr != PHYS_ADDR_MAX)
> > +               memblock_cap_memory_range(0, max_addr);
> > +
> >         if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size)
> {
> >                 /*
> >                  * Add back the memory we just removed if it results
> > in the @@ -427,4 +443,9 @@ void dump_mem_limit(void)
> >         } else {
> >                 pr_emerg("Memory Limit: none\n");
> >         }
> > +
> > +       if (max_addr != PHYS_ADDR_MAX)
> > +               pr_emerg("Max addr: 0x%llx\n", max_addr);
> > +       else
> > +               pr_emerg("Max addr: none\n");
> >  }
> > --
> > 2.25.1
> >
> >
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