Subject: [PATCH v5sub1 8/8] arm64: allow kernel Image to be loaded anywhere in physical memory

From: [email-masked] (Fu Wei)
Date: Tue, 16 Feb 2016 16:55:46 +0800

On 02/02/2016 12:28 AM, Fu Wei wrote:
> Hi Mark
>
> On 02/01/2016 10:50 PM, Mark Rutland wrote:
>> On Mon, Feb 01, 2016 at 11:54:53AM +0100, Ard Biesheuvel wrote:
>>> This relaxes the kernel Image placement requirements, so that it
>>> may be placed at any 2 MB aligned offset in physical memory.
>>>
>>> This is accomplished by ignoring PHYS_OFFSET when installing
>>> memblocks, and accounting for the apparent virtual offset of
>>> the kernel Image. As a result, virtual address references
>>> below PAGE_OFFSET are correctly mapped onto physical references
>>> into the kernel Image regardless of where it sits in memory.
>>>
>>> Note that limiting memory using mem= is not unambiguous anymore after
>>> this change, considering that the kernel may be at the top of physical
>>> memory, and clipping from the bottom rather than the top will discard
>>> any 32-bit DMA addressable memory first. To deal with this, the handling
>>> of mem= is reimplemented to clip top down, but take special care not to
>>> clip memory that covers the kernel image.
>>>
>>> Since mem= should not be considered a production feature, a panic
>>> notifier
>>> handler is installed that dumps the memory limit at panic time if one
>>> was
>>> set.
>>
>> Good idea!
>>
>> It would be great if we could follow up with a sizes.h update for SZ_4G,
>> though that's only a nice-to-have, and in no way should block this.
>>
>> Other than that, this looks good. Thanks for putting this together!
>>
>> Reviewed-by: Mark Rutland <[email-masked]>
>>
>> For the Documentation/arm64 parts we'll need to ask Fu Wei to update the
>> zh_CN/ translation to match.
>
> Great thanks for your info
> Yes, I will working on it

The zh_CN patch has been prepared, once the English version is merged 
into mainline, I will upstream that immediately.
Because there is another zh_CN patch for booting.txt in upstream 
procedure: https://lkml.org/lkml/2016/2/16/164

sorry for delay. :-)

>
>>
>> Mark.
>>
>>>
>>> Signed-off-by: Ard Biesheuvel <[email-masked]>
>>> ---
>>>   Documentation/arm64/booting.txt         |  20 ++--
>>>   arch/arm64/include/asm/boot.h           |   6 ++
>>>   arch/arm64/include/asm/kernel-pgtable.h |  12 +++
>>>   arch/arm64/include/asm/kvm_asm.h        |   2 +-
>>>   arch/arm64/include/asm/memory.h         |  15 +--
>>>   arch/arm64/kernel/head.S                |   6 +-
>>>   arch/arm64/kernel/image.h               |  13 ++-
>>>   arch/arm64/mm/init.c                    | 100 +++++++++++++++++++-
>>>   arch/arm64/mm/mmu.c                     |   3 +
>>>   9 files changed, 155 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/Documentation/arm64/booting.txt
>>> b/Documentation/arm64/booting.txt
>>> index 701d39d3171a..56d6d8b796db 100644
>>> --- a/Documentation/arm64/booting.txt
>>> +++ b/Documentation/arm64/booting.txt
>>> @@ -109,7 +109,13 @@ Header notes:
>>>               1 - 4K
>>>               2 - 16K
>>>               3 - 64K
>>> -  Bits 3-63:    Reserved.
>>> +  Bit 3:    Kernel physical placement
>>> +            0 - 2MB aligned base should be as close as possible
>>> +                to the base of DRAM, since memory below it is not
>>> +                accessible via the linear mapping
>>> +            1 - 2MB aligned base may be anywhere in physical
>>> +                memory
>>> +  Bits 4-63:    Reserved.
>>>
>>>   - When image_size is zero, a bootloader should attempt to keep as much
>>>     memory as possible free for use by the kernel immediately after the
>>> @@ -117,14 +123,14 @@ Header notes:
>>>     depending on selected features, and is effectively unbound.
>>>
>>>   The Image must be placed text_offset bytes from a 2MB aligned base
>>> -address near the start of usable system RAM and called there. Memory
>>> -below that base address is currently unusable by Linux, and
>>> therefore it
>>> -is strongly recommended that this location is the start of system RAM.
>>> -The region between the 2 MB aligned base address and the start of the
>>> -image has no special significance to the kernel, and may be used for
>>> -other purposes.
>>> +address anywhere in usable system RAM and called there. The region
>>> +between the 2 MB aligned base address and the start of the image has no
>>> +special significance to the kernel, and may be used for other purposes.
>>>   At least image_size bytes from the start of the image must be free for
>>>   use by the kernel.
>>> +NOTE: versions prior to v4.6 cannot make use of memory below the
>>> +physical offset of the Image so it is recommended that the Image be
>>> +placed as close as possible to the start of system RAM.
>>>
>>>   Any memory described to the kernel (even that below the start of the
>>>   image) which is not marked as reserved from the kernel (e.g., with a
>>> diff --git a/arch/arm64/include/asm/boot.h
>>> b/arch/arm64/include/asm/boot.h
>>> index 81151b67b26b..ebf2481889c3 100644
>>> --- a/arch/arm64/include/asm/boot.h
>>> +++ b/arch/arm64/include/asm/boot.h
>>> @@ -11,4 +11,10 @@
>>>   #define MIN_FDT_ALIGN        8
>>>   #define MAX_FDT_SIZE        SZ_2M
>>>
>>> +/*
>>> + * arm64 requires the kernel image to placed
>>> + * TEXT_OFFSET bytes beyond a 2 MB aligned base
>>> + */
>>> +#define MIN_KIMG_ALIGN        SZ_2M
>>> +
>>>   #endif
>>> diff --git a/arch/arm64/include/asm/kernel-pgtable.h
>>> b/arch/arm64/include/asm/kernel-pgtable.h
>>> index a459714ee29e..5c6375d8528b 100644
>>> --- a/arch/arm64/include/asm/kernel-pgtable.h
>>> +++ b/arch/arm64/include/asm/kernel-pgtable.h
>>> @@ -79,5 +79,17 @@
>>>   #define SWAPPER_MM_MMUFLAGS    (PTE_ATTRINDX(MT_NORMAL) |
>>> SWAPPER_PTE_FLAGS)
>>>   #endif
>>>
>>> +/*
>>> + * To make optimal use of block mappings when laying out the linear
>>> + * mapping, round down the base of physical memory to a size that can
>>> + * be mapped efficiently, i.e., either PUD_SIZE (4k granule) or
>>> PMD_SIZE
>>> + * (64k granule), or a multiple that can be mapped using contiguous
>>> bits
>>> + * in the page tables: 32 * PMD_SIZE (16k granule)
>>> + */
>>> +#ifdef CONFIG_ARM64_64K_PAGES
>>> +#define ARM64_MEMSTART_ALIGN    SZ_512M
>>> +#else
>>> +#define ARM64_MEMSTART_ALIGN    SZ_1G
>>> +#endif
>>>
>>>   #endif    /* __ASM_KERNEL_PGTABLE_H */
>>> diff --git a/arch/arm64/include/asm/kvm_asm.h
>>> b/arch/arm64/include/asm/kvm_asm.h
>>> index f5aee6e764e6..054ac25e7c2e 100644
>>> --- a/arch/arm64/include/asm/kvm_asm.h
>>> +++ b/arch/arm64/include/asm/kvm_asm.h
>>> @@ -26,7 +26,7 @@
>>>   #define KVM_ARM64_DEBUG_DIRTY_SHIFT    0
>>>   #define KVM_ARM64_DEBUG_DIRTY        (1 <<
>>> KVM_ARM64_DEBUG_DIRTY_SHIFT)
>>>
>>> -#define kvm_ksym_ref(sym)        ((void *)&sym - KIMAGE_VADDR +
>>> PAGE_OFFSET)
>>> +#define kvm_ksym_ref(sym)        phys_to_virt((u64)&sym -
>>> kimage_voffset)
>>>
>>>   #ifndef __ASSEMBLY__
>>>   struct kvm;
>>> diff --git a/arch/arm64/include/asm/memory.h
>>> b/arch/arm64/include/asm/memory.h
>>> index 4388651d1f0d..61005e7dd6cb 100644
>>> --- a/arch/arm64/include/asm/memory.h
>>> +++ b/arch/arm64/include/asm/memory.h
>>> @@ -88,10 +88,10 @@
>>>   #define __virt_to_phys(x) ({                        \
>>>       phys_addr_t __x = (phys_addr_t)(x);                \
>>>       __x >= PAGE_OFFSET ? (__x - PAGE_OFFSET + PHYS_OFFSET) :    \
>>> -                 (__x - KIMAGE_VADDR + PHYS_OFFSET); })
>>> +                 (__x - kimage_voffset); })
>>>
>>>   #define __phys_to_virt(x)    ((unsigned long)((x) - PHYS_OFFSET +
>>> PAGE_OFFSET))
>>> -#define __phys_to_kimg(x)    ((unsigned long)((x) - PHYS_OFFSET +
>>> KIMAGE_VADDR))
>>> +#define __phys_to_kimg(x)    ((unsigned long)((x) + kimage_voffset))
>>>
>>>   /*
>>>    * Convert a page to/from a physical address
>>> @@ -127,13 +127,14 @@ extern phys_addr_t        memstart_addr;
>>>   /* PHYS_OFFSET - the physical address of the start of memory. */
>>>   #define PHYS_OFFSET        ({ memstart_addr; })
>>>
>>> +/* the offset between the kernel virtual and physical mappings */
>>> +extern u64            kimage_voffset;
>>> +
>>>   /*
>>> - * The maximum physical address that the linear direct mapping
>>> - * of system RAM can cover. (PAGE_OFFSET can be interpreted as
>>> - * a 2's complement signed quantity and negated to derive the
>>> - * maximum size of the linear mapping.)
>>> + * Allow all memory at the discovery stage. We will clip it later.
>>>    */
>>> -#define MAX_MEMBLOCK_ADDR    ({ memstart_addr - PAGE_OFFSET - 1; })
>>> +#define MIN_MEMBLOCK_ADDR    0
>>> +#define MAX_MEMBLOCK_ADDR    U64_MAX
>>>
>>>   /*
>>>    * PFNs are used to describe any physical page; this means
>>> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
>>> index 04d38a058b19..05b98289093e 100644
>>> --- a/arch/arm64/kernel/head.S
>>> +++ b/arch/arm64/kernel/head.S
>>> @@ -428,7 +428,11 @@ __mmap_switched:
>>>       and    x4, x4, #~(THREAD_SIZE - 1)
>>>       msr    sp_el0, x4            // Save thread_info
>>>       str_l    x21, __fdt_pointer, x5        // Save FDT pointer
>>> -    str_l    x24, memstart_addr, x6        // Save PHYS_OFFSET
>>> +
>>> +    ldr    x4, =KIMAGE_VADDR        // Save the offset between
>>> +    sub    x4, x4, x24            // the kernel virtual and
>>> +    str_l    x4, kimage_voffset, x5        // physical mappings
>>> +
>>>       mov    x29, #0
>>>   #ifdef CONFIG_KASAN
>>>       bl    kasan_early_init
>>> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
>>> index 999633bd7294..c9c62cab25a4 100644
>>> --- a/arch/arm64/kernel/image.h
>>> +++ b/arch/arm64/kernel/image.h
>>> @@ -42,15 +42,18 @@
>>>   #endif
>>>
>>>   #ifdef CONFIG_CPU_BIG_ENDIAN
>>> -#define __HEAD_FLAG_BE    1
>>> +#define __HEAD_FLAG_BE        1
>>>   #else
>>> -#define __HEAD_FLAG_BE    0
>>> +#define __HEAD_FLAG_BE        0
>>>   #endif
>>>
>>> -#define __HEAD_FLAG_PAGE_SIZE ((PAGE_SHIFT - 10) / 2)
>>> +#define __HEAD_FLAG_PAGE_SIZE    ((PAGE_SHIFT - 10) / 2)
>>>
>>> -#define __HEAD_FLAGS    ((__HEAD_FLAG_BE << 0) |    \
>>> -             (__HEAD_FLAG_PAGE_SIZE << 1))
>>> +#define __HEAD_FLAG_PHYS_BASE    1
>>> +
>>> +#define __HEAD_FLAGS        ((__HEAD_FLAG_BE << 0) |    \
>>> +                 (__HEAD_FLAG_PAGE_SIZE << 1) |    \
>>> +                 (__HEAD_FLAG_PHYS_BASE << 3))
>>>
>>>   /*
>>>    * These will output as part of the Image header, which should be
>>> little-endian
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index 1d627cd8121c..e8e853a1024c 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -35,8 +35,10 @@
>>>   #include <linux/efi.h>
>>>   #include <linux/swiotlb.h>
>>>
>>> +#include <asm/boot.h>
>>>   #include <asm/fixmap.h>
>>>   #include <asm/kasan.h>
>>> +#include <asm/kernel-pgtable.h>
>>>   #include <asm/memory.h>
>>>   #include <asm/sections.h>
>>>   #include <asm/setup.h>
>>> @@ -158,9 +160,80 @@ static int __init early_mem(char *p)
>>>   }
>>>   early_param("mem", early_mem);
>>>
>>> +/*
>>> + * clip_mem_range() - remove memblock memory between @min and @max
>>> until
>>> + *                    we meet the limit in 'memory_limit'.
>>> + */
>>> +static void __init clip_mem_range(u64 min, u64 max)
>>> +{
>>> +    u64 mem_size, to_remove;
>>> +    int i;
>>> +
>>> +again:
>>> +    mem_size = memblock_phys_mem_size();
>>> +    if (mem_size <= memory_limit || max <= min)
>>> +        return;
>>> +
>>> +    to_remove = mem_size - memory_limit;
>>> +
>>> +    for (i = memblock.memory.cnt - 1; i >= 0; i--) {
>>> +        struct memblock_region *r = memblock.memory.regions + i;
>>> +        u64 start = max(min, r->base);
>>> +        u64 end = min(max, r->base + r->size);
>>> +
>>> +        if (start >= max || end <= min)
>>> +            continue;
>>> +
>>> +        if (end > min) {
>>> +            u64 size = min(to_remove, end - max(start, min));
>>> +
>>> +            memblock_remove(end - size, size);
>>> +        } else {
>>> +            memblock_remove(start, min(max - start, to_remove));
>>> +        }
>>> +        goto again;
>>> +    }
>>> +}
>>> +
>>>   void __init arm64_memblock_init(void)
>>>   {
>>> -    memblock_enforce_memory_limit(memory_limit);
>>> +    const s64 linear_region_size = -(s64)PAGE_OFFSET;
>>> +
>>> +    /*
>>> +     * Select a suitable value for the base of physical memory.
>>> +     */
>>> +    memstart_addr = round_down(memblock_start_of_DRAM(),
>>> +                   ARM64_MEMSTART_ALIGN);
>>> +
>>> +    /*
>>> +     * Remove the memory that we will not be able to cover with the
>>> +     * linear mapping. Take care not to clip the kernel which may be
>>> +     * high in memory.
>>> +     */
>>> +    memblock_remove(max(memstart_addr + linear_region_size,
>>> __pa(_end)),
>>> +            ULLONG_MAX);
>>> +    if (memblock_end_of_DRAM() > linear_region_size)
>>> +        memblock_remove(0, memblock_end_of_DRAM() -
>>> linear_region_size);
>>> +
>>> +    if (memory_limit != (phys_addr_t)ULLONG_MAX) {
>>> +        u64 kbase = round_down(__pa(_text), MIN_KIMG_ALIGN);
>>> +        u64 kend = PAGE_ALIGN(__pa(_end));
>>> +        u64 const sz_4g = 0x100000000UL;
>>> +
>>> +        /*
>>> +         * Clip memory in order of preference:
>>> +         * - above the kernel and above 4 GB
>>> +         * - between 4 GB and the start of the kernel (if the kernel
>>> +         *   is loaded high in memory)
>>> +         * - between the kernel and 4 GB (if the kernel is loaded
>>> +         *   low in memory)
>>> +         * - below 4 GB
>>> +         */
>>> +        clip_mem_range(max(sz_4g, kend), ULLONG_MAX);
>>> +        clip_mem_range(sz_4g, kbase);
>>> +        clip_mem_range(kend, sz_4g);
>>> +        clip_mem_range(0, min(kbase, sz_4g));
>>> +    }
>>>
>>>       /*
>>>        * Register the kernel text, kernel data, initrd, and initial
>>> @@ -381,3 +454,28 @@ static int __init keepinitrd_setup(char *__unused)
>>>
>>>   __setup("keepinitrd", keepinitrd_setup);
>>>   #endif
>>> +
>>> +/*
>>> + * Dump out memory limit information on panic.
>>> + */
>>> +static int dump_mem_limit(struct notifier_block *self, unsigned long
>>> v, void *p)
>>> +{
>>> +    if (memory_limit != (phys_addr_t)ULLONG_MAX) {
>>> +        pr_emerg("Memory Limit: %llu MB\n", memory_limit >> 20);
>>> +    } else {
>>> +        pr_emerg("Memory Limit: none\n");
>>> +    }
>>> +    return 0;
>>> +}
>>> +
>>> +static struct notifier_block mem_limit_notifier = {
>>> +    .notifier_call = dump_mem_limit,
>>> +};
>>> +
>>> +static int __init register_mem_limit_dumper(void)
>>> +{
>>> +    atomic_notifier_chain_register(&panic_notifier_list,
>>> +                       &mem_limit_notifier);
>>> +    return 0;
>>> +}
>>> +__initcall(register_mem_limit_dumper);
>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>>> index 4c4b15932963..8dda38378959 100644
>>> --- a/arch/arm64/mm/mmu.c
>>> +++ b/arch/arm64/mm/mmu.c
>>> @@ -46,6 +46,9 @@
>>>
>>>   u64 idmap_t0sz = TCR_T0SZ(VA_BITS);
>>>
>>> +u64 kimage_voffset __read_mostly;
>>> +EXPORT_SYMBOL(kimage_voffset);
>>> +
>>>   /*
>>>    * Empty_zero_page is a special page that is used for
>>> zero-initialized data
>>>    * and COW.
>>> --
>>> 2.5.0
>>>