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Message-ID: <54773d69-1a2b-1ab3-24d9-b322d580fb42@oracle.com>
Date: Mon, 11 May 2020 16:29:33 -0700
From: Anthony Yznaga <anthony.yznaga@...cle.com>
To: Mike Rapoport <rppt@...ux.ibm.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
willy@...radead.org, corbet@....net, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
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masahiroy@...nel.org, ardb@...nel.org, ndesaulniers@...gle.com,
dima@...ovin.in, daniel.kiper@...cle.com, nivedita@...m.mit.edu,
rafael.j.wysocki@...el.com, dan.j.williams@...el.com,
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andriy.shevchenko@...ux.intel.com, keescook@...omium.org,
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ying.huang@...el.com, yang.shi@...ux.alibaba.com,
gustavo@...eddedor.com, ziqian.lzq@...fin.com,
vdavydov.dev@...il.com, jason.zeng@...el.com, kevin.tian@...el.com,
zhiyuan.lv@...el.com, lei.l.li@...el.com, paul.c.lai@...el.com,
ashok.raj@...el.com, linux-fsdevel@...r.kernel.org,
linux-doc@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [RFC 14/43] mm: memblock: PKRAM: prevent memblock resize from
clobbering preserved pages
On 5/11/20 6:57 AM, Mike Rapoport wrote:
> On Wed, May 06, 2020 at 05:41:40PM -0700, Anthony Yznaga wrote:
>> The size of the memblock reserved array may be increased while preserved
>> pages are being reserved. When this happens, preserved pages that have
>> not yet been reserved are at risk for being clobbered when space for a
>> larger array is allocated.
>> When called from memblock_double_array(), a wrapper around
>> memblock_find_in_range() walks the preserved pages pagetable to find
>> sufficiently sized ranges without preserved pages and passes them to
>> memblock_find_in_range().
> I'd suggest to create an array of memblock_region's that will contain
> the PKRAM ranges before kexec and pass this array to the new kernel.
> Then, somewhere in start_kerenel() replace replace
> memblock.reserved->regions with that array.
I'll look into doing this. Thanks!
Anthony
>
>> Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
>> ---
>> include/linux/pkram.h | 3 +++
>> mm/memblock.c | 15 +++++++++++++--
>> mm/pkram.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 67 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/pkram.h b/include/linux/pkram.h
>> index edc5d8bef9d3..409022e1472f 100644
>> --- a/include/linux/pkram.h
>> +++ b/include/linux/pkram.h
>> @@ -62,6 +62,9 @@ struct page *pkram_load_page(struct pkram_stream *ps, unsigned long *index,
>> ssize_t pkram_write(struct pkram_stream *ps, const void *buf, size_t count);
>> size_t pkram_read(struct pkram_stream *ps, void *buf, size_t count);
>>
>> +phys_addr_t pkram_memblock_find_in_range(phys_addr_t start, phys_addr_t end,
>> + phys_addr_t size, phys_addr_t align);
>> +
>> #ifdef CONFIG_PKRAM
>> extern unsigned long pkram_reserved_pages;
>> void pkram_reserve(void);
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index c79ba6f9920c..69ae883b8d21 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -16,6 +16,7 @@
>> #include <linux/kmemleak.h>
>> #include <linux/seq_file.h>
>> #include <linux/memblock.h>
>> +#include <linux/pkram.h>
>>
>> #include <asm/sections.h>
>> #include <linux/io.h>
>> @@ -349,6 +350,16 @@ phys_addr_t __init_memblock memblock_find_in_range(phys_addr_t start,
>> return ret;
>> }
>>
>> +phys_addr_t __init_memblock __memblock_find_in_range(phys_addr_t start,
>> + phys_addr_t end, phys_addr_t size,
>> + phys_addr_t align)
>> +{
>> + if (IS_ENABLED(CONFIG_PKRAM))
>> + return pkram_memblock_find_in_range(start, end, size, align);
>> + else
>> + return memblock_find_in_range(start, end, size, align);
>> +}
>> +
>> static void __init_memblock memblock_remove_region(struct memblock_type *type, unsigned long r)
>> {
>> type->total_size -= type->regions[r].size;
>> @@ -447,11 +458,11 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
>> if (type != &memblock.reserved)
>> new_area_start = new_area_size = 0;
>>
>> - addr = memblock_find_in_range(new_area_start + new_area_size,
>> + addr = __memblock_find_in_range(new_area_start + new_area_size,
>> memblock.current_limit,
>> new_alloc_size, PAGE_SIZE);
>> if (!addr && new_area_size)
>> - addr = memblock_find_in_range(0,
>> + addr = __memblock_find_in_range(0,
>> min(new_area_start, memblock.current_limit),
>> new_alloc_size, PAGE_SIZE);
>>
>> diff --git a/mm/pkram.c b/mm/pkram.c
>> index dd3c89614010..e49c9bcd3854 100644
>> --- a/mm/pkram.c
>> +++ b/mm/pkram.c
>> @@ -1238,3 +1238,54 @@ void pkram_free_pgt(void)
>> __free_pages_core(virt_to_page(pkram_pgd), 0);
>> pkram_pgd = NULL;
>> }
>> +
>> +static int __init_memblock pkram_memblock_find_cb(struct pkram_pg_state *st, unsigned long base, unsigned long size)
>> +{
>> + unsigned long end = base + size;
>> + unsigned long addr;
>> +
>> + if (size < st->min_size)
>> + return 0;
>> +
>> + addr = memblock_find_in_range(base, end, st->min_size, PAGE_SIZE);
>> + if (!addr)
>> + return 0;
>> +
>> + st->retval = addr;
>> + return 1;
>> +}
>> +
>> +/*
>> + * It may be necessary to allocate a larger reserved memblock array
>> + * while populating it with ranges of preserved pages. To avoid
>> + * trampling preserved pages that have not yet been added to the
>> + * memblock reserved list this function implements a wrapper around
>> + * memblock_find_in_range() that restricts searches to subranges
>> + * that do not contain preserved pages.
>> + */
>> +phys_addr_t __init_memblock pkram_memblock_find_in_range(phys_addr_t start,
>> + phys_addr_t end, phys_addr_t size,
>> + phys_addr_t align)
>> +{
>> + struct pkram_pg_state st = {
>> + .range_cb = pkram_memblock_find_cb,
>> + .min_addr = start,
>> + .max_addr = end,
>> + .min_size = PAGE_ALIGN(size),
>> + .find_holes = true,
>> + };
>> +
>> + if (!pkram_reservation_in_progress)
>> + return memblock_find_in_range(start, end, size, align);
>> +
>> + if (!pkram_pgd) {
>> + WARN_ONCE(1, "No preserved pages pagetable\n");
>> + return memblock_find_in_range(start, end, size, align);
>> + }
>> +
>> + WARN_ONCE(memblock_bottom_up(), "PKRAM: bottom up memblock allocation not yet supported\n");
>> +
>> + pkram_walk_pgt_rev(&st, pkram_pgd);
>> +
>> + return st.retval;
>> +}
>> --
>> 2.13.3
>>
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