Re: [PATCH] makedumpfile: Enable --mem-usage for s390x

[Michael Holzheu <holzheu@linux.vnet.ibm.com>]

Hello Atsushi,

On Thu, 23 Oct 2014 06:56:47 +0000
Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp> wrote:

> >On Tue, 14 Oct 2014 07:19:13 +0000
> >Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp> wrote:

[snip]

> I noticed that is_vmalloc_addr_x86_64() can't be used as is_phys_addr()
> due to the "kaslr issue". I fixed it in the common path as below, but
> --mem-usage still has the same issue since initial() will be invoked
> after get_kcore_dump_loads().
> 
>   http://lists.infradead.org/pipermail/kexec/2014-October/012743.html
> 
> I know it's so late, but I began to think the current implementation
> that invokes vaddr_to_paddr_XXX() before initial() is bad:
> 
> show_mem_usage()
>   + get_kcore_dump_loads()
>     + process_dump_load()
>       + vaddr_to_paddr_XXX()
>   + initial()
>   ...
> vaddr_to_paddr_XXX() does VtoP translation *properly*, so it needs
> several symbols. This design is OK since it's a general method.

So the current implementation that uses vaddr_to_paddr_xxx()
for --mem-usage *before* initial() is broken? Or does it currently
works only by chance?

> OTOH, we need a kludge which can be used under any situations and
> should use it for --mem-usage:
> 
>   VtoP_kludge_s390x(unsigned long vaddr) 
>   {
> 	/* s390 has 1:1 VtoP mapping that starts with zero. */
>   	return vaddr;
>   }
> 
> also x86_64's can be implemented like below:
> 
>   VtoP_kludge_x86_64(unsigned long vaddr) 
>   {
> 	/* if the address is direct mapped, it's easy to translate. */
> 	unsigned long paddr = vaddr - PAGE_OFFSET;
> 	return paddr;
>   }

What about using the kernel name __pa(vaddr)?

[snip]

> >--- a/elf_info.c
> >+++ b/elf_info.c
> >@@ -854,7 +854,7 @@ int get_kcore_dump_loads(void)
> >
> > 	for (i = 0; i < num_pt_loads; ++i) {
> > 		struct pt_load_segment *p = &pt_loads[i];
> >-		if (is_vmalloc_addr(p->virt_start))
> >+		if (!is_phys_addr(p->virt_start))
> 
> This part implicitly does VtoP translation.
> Actually it works for s390x but it's not suitable as a general code,
> so we should use VtoP_kludge(should be better name!) too.
> Then we can use is_iomem_phys_addr() also for other architecture.

So how exactly should the code look like for non s390x architectures?

Michael


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