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    SubjectRe: [PATCH] powerpc: align memory_limit to 16MB in early_parse_mem
    On Mon, Apr 1, 2024 at 10:17 AM Joel Savitz <jsavitz@redhat.com> wrote:
    >
    > On Tue, Mar 26, 2024 at 12:45 AM Joel Savitz <jsavitz@redhat.com> wrote:
    > >
    > > On Fri, Mar 8, 2024 at 5:18 AM Aneesh Kumar K.V <aneesh.kumar@kernel.org> wrote:
    > > >
    > > > Joel Savitz <jsavitz@redhat.com> writes:
    > > >
    > > > > On 64-bit powerpc, usage of a non-16MB-aligned value for the mem= kernel
    > > > > cmdline parameter results in a system hang at boot.
    > > > >
    > > > > For example, using 'mem=4198400K' will always reproduce this issue.
    > > > >
    > > > > This patch fixes the problem by aligning any argument to mem= to 16MB
    > > > > corresponding with the large page size on powerpc.
    > > > >
    > > > > Fixes: 2babf5c2ec2f ("[PATCH] powerpc: Unify mem= handling")
    > > > > Co-developed-by: Gonzalo Siero <gsierohu@redhat.com>
    > > > > Signed-off-by: Gonzalo Siero <gsierohu@redhat.com>
    > > > > Signed-off-by: Joel Savitz <jsavitz@redhat.com>
    > > > > ---
    > > > > arch/powerpc/kernel/prom.c | 6 +++++-
    > > > > 1 file changed, 5 insertions(+), 1 deletion(-)
    > > > >
    > > > > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
    > > > > index 0b5878c3125b..8cd3e2445d8a 100644
    > > > > --- a/arch/powerpc/kernel/prom.c
    > > > > +++ b/arch/powerpc/kernel/prom.c
    > > > > @@ -82,8 +82,12 @@ static int __init early_parse_mem(char *p)
    > > > > {
    > > > > if (!p)
    > > > > return 1;
    > > > > -
    > > > > +#ifdef CONFIG_PPC64
    > > > > + /* Align to 16 MB == size of ppc64 large page */
    > > > > + memory_limit = ALIGN(memparse(p, &p), 0x1000000);
    > > > > +#else
    > > > > memory_limit = PAGE_ALIGN(memparse(p, &p));
    > > > > +#endif
    > > > > DBG("memory limit = 0x%llx\n", memory_limit);
    > > > >
    > > > > return 0;
    > > > > --
    > > > > 2.43.0
    > > >
    > > > Can you try this change?
    > > >
    > > > commit 5555bc55e1aa71f545cff31e1eccdb4a2e39df84
    > > > Author: Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel.org>
    > > > Date: Fri Mar 8 14:45:26 2024 +0530
    > > >
    > > > powerpc/mm: Align memory_limit value specified using mem= kernel parameter
    > > >
    > > > The value specified for the memory limit is used to set a restriction on
    > > > memory usage. It is important to ensure that this restriction is within
    > > > the linear map kernel address space range. The hash page table
    > > > translation uses a 16MB page size to map the kernel linear map address
    > > > space. htab_bolt_mapping() function aligns down the size of the range
    > > > while mapping kernel linear address space. Since the memblock limit is
    > > > enforced very early during boot, before we can detect the type of memory
    > > > translation (radix vs hash), we align the memory limit value specified
    > > > as a kernel parameter to 16MB. This alignment value will work for both
    > > > hash and radix translations.
    > > >
    > > > Signed-off-by: Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel.org>
    > > >
    > > > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
    > > > index 0b5878c3125b..9bd965d35352 100644
    > > > --- a/arch/powerpc/kernel/prom.c
    > > > +++ b/arch/powerpc/kernel/prom.c
    > > > @@ -824,8 +824,11 @@ void __init early_init_devtree(void *params)
    > > > reserve_crashkernel();
    > > > early_reserve_mem();
    > > >
    > > > - /* Ensure that total memory size is page-aligned. */
    > > > - limit = ALIGN(memory_limit ?: memblock_phys_mem_size(), PAGE_SIZE);
    > > > + if (memory_limit > memblock_phys_mem_size())
    > > > + memory_limit = 0;
    > > > +
    > > > + /* Align down to 16 MB which is large page size with hash page translation */
    > > > + limit = ALIGN_DOWN(memory_limit ?: memblock_phys_mem_size(), SZ_16M);
    > > > memblock_enforce_memory_limit(limit);
    > > >
    > > > #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_PPC_4K_PAGES)
    > > > diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
    > > > index e67effdba85c..d6410549e141 100644
    > > > --- a/arch/powerpc/kernel/prom_init.c
    > > > +++ b/arch/powerpc/kernel/prom_init.c
    > > > @@ -817,8 +817,8 @@ static void __init early_cmdline_parse(void)
    > > > opt += 4;
    > > > prom_memory_limit = prom_memparse(opt, (const char **)&opt);
    > > > #ifdef CONFIG_PPC64
    > > > - /* Align to 16 MB == size of ppc64 large page */
    > > > - prom_memory_limit = ALIGN(prom_memory_limit, 0x1000000);
    > > > + /* Align down to 16 MB which is large page size with hash page translation */
    > > > + prom_memory_limit = ALIGN_DOWN(prom_memory_limit, SZ_16M);
    > > > #endif
    > > > }
    > > >
    > > >
    > >
    > > Sorry for the delayed reply. I just tested this patch and it fixes the
    > > bug for me.
    >
    > Hi,
    >
    > Just a quick follow up on this.
    >
    > The above patch fixed the bug for me.
    >
    > How do we want to proceed?
    >
    > Best,
    > Joel Savitz

    Hi,

    I haven't heard anything on this thread so I'm just sending a quick follow up.

    Do we want to merge this

    Best,
    Joel Savitz


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