linux-kernel - Re: [PATCH 2/2] efi: Don't add memblocks for unusable memory

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Date: Fri, 2 Feb 2024 12:41:04 -0500
From: Andrew Bresticker <abrestic@...osinc.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 2/2] efi: Don't add memblocks for unusable memory

On Fri, Feb 2, 2024 at 11:45 AM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Fri, 2 Feb 2024 at 17:34, Andrew Bresticker <abrestic@...osinc.com> wrote:
> >
> > Adding memblocks (even if nomap) for such regions unnecessarily consumes
> > resources by creating struct pages for memory that may never be used or,
> > in the case of soft-reserved regions, prevents the memory from later
> > being hotplugged in by dax_kmem. This is also consistent with how x86
> > handles unusable memory found in the EFI memory map.
> >
>
> x86 doesn't care as much about memory vs device semantics as ARM does.
>
> This affects the output of memblock_is_[region_]memory(), so we'd have
> to double check that none of those uses get broken by this.
>
> If the soft reserved regions need to be omitted from memblock, we can
> deal with that separately perhaps, but changing it at this level seems
> inappropriate to me.

Sure, I can constrain this to just the soft-reserved regions.

-Andrew

>
>
> > Signed-off-by: Andrew Bresticker <abrestic@...osinc.com>
> > ---
> >  drivers/firmware/efi/efi-init.c | 12 +-----------
> >  1 file changed, 1 insertion(+), 11 deletions(-)
> >
> > diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c
> > index d4987d013080..f05bacac89b7 100644
> > --- a/drivers/firmware/efi/efi-init.c
> > +++ b/drivers/firmware/efi/efi-init.c
> > @@ -24,13 +24,6 @@
> >
> >  unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;
> >
> > -static int __init is_memory(efi_memory_desc_t *md)
> > -{
> > -       if (md->attribute & (EFI_MEMORY_WB|EFI_MEMORY_WT|EFI_MEMORY_WC))
> > -               return 1;
> > -       return 0;
> > -}
> > -
> >  /*
> >   * Translate a EFI virtual address into a physical address: this is necessary,
> >   * as some data members of the EFI system table are virtually remapped after
> > @@ -195,12 +188,9 @@ static __init void reserve_regions(void)
> >                 memrange_efi_to_native(&paddr, &npages);
> >                 size = npages << PAGE_SHIFT;
> >
> > -               if (is_memory(md)) {
> > +               if (is_usable_memory(md)) {
> >                         early_init_dt_add_memory_arch(paddr, size);
> >
> > -                       if (!is_usable_memory(md))
> > -                               memblock_mark_nomap(paddr, size);
> > -
> >                         /* keep ACPI reclaim memory intact for kexec etc. */
> >                         if (md->type == EFI_ACPI_RECLAIM_MEMORY)
> >                                 memblock_reserve(paddr, size);
> > --
> > 2.34.1
> >