Hi Will,
On Tue, Feb 15, 2022 at 04:44:23PM +0000, Will Deacon wrote:
> On Wed, Feb 09, 2022 at 09:26:42AM +0000, Huang Shijie wrote:
> > The following interrelated ranges are needed by the kdump crash tool:
> > MODULES_VADDR ~ MODULES_END,
> > VMALLOC_START ~ VMALLOC_END,
> > VMEMMAP_START ~ VMEMMAP_END
> >
> > Since these values change from time to time, it is preferable to export
> > them via vmcoreinfo than to change the crash's code frequently.
>
> Please can you explain _why_ they are needed?
The current Crash code is still based at kernel v4.9.
The virtual memory layout looks like this:
+--------------------------------------------------------------------+
| KASAN | MODULE | VMALLOC | .... | VMEMMAP |
+--------------------------------------------------------------------+
The Crash uses MODULES range to set the VMALLOC ranges.
If the ranges are wrong, Crash will _NOT_ works well for some latest kernel
,such as v5.11 later. (Please correct me if I am wrong).
It seems the VMEMMAP range is less important.
I list all the changes since v4.9 to now:
1.) The current crash code is based at kernel v4.9.
The virtual memory layout looks like this:
+--------------------------------------------------------------------+
| KASAN | MODULE | VMALLOC | .... | VMEMMAP |
+--------------------------------------------------------------------+
The macros are:
#define MODULES_VADDR (VA_START + KASAN_SHADOW_SIZE)
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
#define VMEMMAP_START (PAGE_OFFSET - VMEMMAP_SIZE)
2.) In the kernel v5.0, the patch will add a new BFP JIT region:
"91fc957c9b1d arm64/bpf: don't allocate BPF JIT programs in module memory"
The virtual memory layout looks like this:
+--------------------------------------------------------------------+
| KASAN | BPF_JIT | MODULE | VMALLOC | .... | VMEMMAP |
+--------------------------------------------------------------------+
The macros are:
#define MODULES_VADDR (BPF_JIT_REGION_END)
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
#define VMEMMAP_START (PAGE_OFFSET - VMEMMAP_SIZE)
The layout does not changed until v5.4.
3.) In the kernel v5.4, several patches changes the layout, such as:
"ce3aaed87344 arm64: mm: Modify calculation of VMEMMAP_SIZE"
"14c127c957c1 arm64: mm: Flip kernel VA space"
and the virtual memory layout looks like this:
+--------------------------------------------------------------------+
| KASAN | BPF_JIT | MODULE | VMALLOC | .... | VMEMMAP |
+--------------------------------------------------------------------+
The macros are:
#define MODULES_VADDR (BPF_JIT_REGION_END)
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (- PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
#define VMEMMAP_START (-VMEMMAP_SIZE - SZ_2M)
4.) In the kernel v5.11, several patches changes the layout, such as:
"9ad7c6d5e75b arm64: mm: tidy up top of kernel VA space"
"f4693c2716b3 arm64: mm: extend linear region for 52-bit VA configurations"
and the virtual memory layout looks like this:
+--------------------------------------------------------------------+
| BPF_JIT | MODULE | VMALLOC | .... | VMEMMAP |
+--------------------------------------------------------------------+
The macros are:
#define MODULES_VADDR (BPF_JIT_REGION_END)
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (VMEMMAP_START - SZ_256M)
#define VMEMMAP_START (-(UL(1) << (VA_BITS - VMEMMAP_SHIFT)))
#define VMEMMAP_END (VMEMMAP_START + VMEMMAP_SIZE)
5.) In the kernel v5.16, after the patch
"b89ddf4cca43 arm64/bpf: Remove 128MB limit for BPF JIT programs"
the virtual memory layout looks like this:
+--------------------------------------------------------------------+
| MODULE | VMALLOC | .... | VMEMMAP |
+--------------------------------------------------------------------+
The macros are:
#define MODULES_VADDR (_PAGE_END(VA_BITS_MIN))
#define MODULES_END (MODULES_VADDR + MODULES_VSIZE)
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (VMEMMAP_START - SZ_256M)
#define VMEMMAP_START (-(UL(1) << (VA_BITS - VMEMMAP_SHIFT)))
#define VMEMMAP_END (VMEMMAP_START + VMEMMAP_SIZE)
BTW:I am currently coding a patch for the Crash to update all the ranges to
the latest kernel version v5.17-rc4.
Thanks
Huang Shijie
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