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

[Mike Rapoport <rppt@kernel.org>]

On Wed, Dec 15, 2021 at 09:30:36AM +0000, Peng Fan wrote:
> > Subject: Re: [PATCH 2/2] arm64: mm: support bootparam max_addr
> > 
> > On Wed, Dec 15, 2021 at 07:59:45AM +0000, Peng Fan wrote:
> > > > Subject: Re: [PATCH 2/2] arm64: mm: support bootparam max_addr
> > > >
> > > > On Wed, 15 Dec 2021 at 07:56, Peng Fan (OSS) <peng.fan@oss.nxp.com>
> > > > wrote:
> > > > >
> > > > > From: Peng Fan <peng.fan@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@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.
> > 
> > request_mem_region() is for MMIO.  Why do you want to use it for RAM?
> 
> + Jan, the jailhouse hypervisor owner.
> 
> There is an out of tree driver
> https://github.com/siemens/jailhouse/blob/master/driver/main.c#L466
> 
> The hypervisor jailhouse is loaded after linux boot up, and the hypervisor
> bin file needs to be loaded into DRAM that reserved in our device
> tree with node with no map property.
> 
> And the hypervisor use virtual pci for communication between VMs,
> The virtual pci use part of the reserved DRAM area as PCI MMIO space.
> 
> Maybe I should use /memreserve, but not node with no-map property.

So, my understanding is that you need a chunk of memory that Linux does not
use and does not map into the kernel page tables.
In that case /memreserve + nomap in the device tree could be a better
solution than mem=X.
 
> Thanks,
> Peng.
> 
> > 
> > > 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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> > 
> > --
> > Sincerely yours,
> > Mike.

-- 
Sincerely yours,
Mike.

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