linux-kernel - Re: [PATCH 10/12] mips: Print the kernel virtual mem layout on debugging

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Date:   Wed, 24 Apr 2019 17:35:11 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Matt Redfearn <matt.redfearn@...s.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Bogendoerfer <tbogendoerfer@...e.de>,
        Huacai Chen <chenhc@...ote.com>,
        Stefan Agner <stefan@...er.ch>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Juergen Gross <jgross@...e.com>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/12] mips: Print the kernel virtual mem layout on
 debugging

On Wed, Apr 24, 2019 at 04:47:11PM +0300, Mike Rapoport wrote:
> On Wed, Apr 24, 2019 at 01:47:46AM +0300, Serge Semin wrote:
> > It is useful at least for debugging to have the kernel virtual
> > memory layout printed at boot time so to have the full information
> > about the booted kernel. Make the printing optional and available
> > only when DEBUG_KERNEL config is enabled so not to leak a sensitive
> > kernel information.
> > 
> > Signed-off-by: Serge Semin <fancer.lancer@...il.com>
> > ---
> >  arch/mips/mm/init.c | 49 +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> > 
> > diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
> > index bbb196ad5f26..c338bbd03b2a 100644
> > --- a/arch/mips/mm/init.c
> > +++ b/arch/mips/mm/init.c
> > @@ -31,6 +31,7 @@
> >  #include <linux/gfp.h>
> >  #include <linux/kcore.h>
> >  #include <linux/initrd.h>
> > +#include <linux/sizes.h>
> >  
> >  #include <asm/bootinfo.h>
> >  #include <asm/cachectl.h>
> > @@ -56,6 +57,53 @@ unsigned long empty_zero_page, zero_page_mask;
> >  EXPORT_SYMBOL_GPL(empty_zero_page);
> >  EXPORT_SYMBOL(zero_page_mask);
> >  
> > +/*
> > + * Print out the kernel virtual memory layout
> > + */
> > +#define MLK(b, t) (void *)b, (void *)t, ((t) - (b)) >> 10
> > +#define MLM(b, t) (void *)b, (void *)t, ((t) - (b)) >> 20
> > +#define MLK_ROUNDUP(b, t) (void *)b, (void *)t, DIV_ROUND_UP(((t) - (b)), SZ_1K)
> > +static void __init mem_print_kmap_info(void)
> > +{
> > +#ifdef CONFIG_DEBUG_KERNEL
> 
> Maybe CONFIG_DEBUG_VM?
> 

Last time I posted this patch Matt suggested to use CONFIG_DEBUG_KERNEL [1].
On the other hand arm platform prints this table unconditionally, but uses %lx
format for low-memory ranges and %p for kernel segments. I even more inclined
in the arm solution. But if selecting between DEBUG_KERNEL and DEBUG_VM I'd
stick with DEBUG_KERNEL, since VM-debug config help text states it is
intended for special performance checks: "Enable this to turn on extended
checks in the virtual-memory system that may impact performance," and
not for memory layout.

-Sergey

[1] https://lkml.org/lkml/2018/2/13/494

> > +	pr_notice("Kernel virtual memory layout:\n"
> > +		  "    lowmem  : 0x%px - 0x%px  (%4ld MB)\n"
> > +		  "      .text : 0x%px - 0x%px  (%4td kB)\n"
> > +		  "      .data : 0x%px - 0x%px  (%4td kB)\n"
> > +		  "      .init : 0x%px - 0x%px  (%4td kB)\n"
> > +		  "      .bss  : 0x%px - 0x%px  (%4td kB)\n"
> > +		  "    vmalloc : 0x%px - 0x%px  (%4ld MB)\n"
> > +#ifdef CONFIG_HIGHMEM
> > +		  "    pkmap   : 0x%px - 0x%px  (%4ld MB)\n"
> > +#endif
> > +		  "    fixmap  : 0x%px - 0x%px  (%4ld kB)\n",
> > +		  MLM(PAGE_OFFSET, (unsigned long)high_memory),
> > +		  MLK_ROUNDUP(_text, _etext),
> > +		  MLK_ROUNDUP(_sdata, _edata),
> > +		  MLK_ROUNDUP(__init_begin, __init_end),
> > +		  MLK_ROUNDUP(__bss_start, __bss_stop),
> > +		  MLM(VMALLOC_START, VMALLOC_END),
> > +#ifdef CONFIG_HIGHMEM
> > +		  MLM(PKMAP_BASE, (PKMAP_BASE) + (LAST_PKMAP)*(PAGE_SIZE)),
> > +#endif
> > +		  MLK(FIXADDR_START, FIXADDR_TOP));
> > +
> > +	/* Check some fundamental inconsistencies. May add something else? */
> > +#ifdef CONFIG_HIGHMEM
> > +	BUILD_BUG_ON(VMALLOC_END < PAGE_OFFSET);
> > +	BUG_ON(VMALLOC_END < (unsigned long)high_memory);
> > +	BUILD_BUG_ON((PKMAP_BASE) + (LAST_PKMAP)*(PAGE_SIZE) < PAGE_OFFSET);
> > +	BUG_ON((PKMAP_BASE) + (LAST_PKMAP)*(PAGE_SIZE) <
> > +		(unsigned long)high_memory);
> > +#endif
> > +	BUILD_BUG_ON(FIXADDR_TOP < PAGE_OFFSET);
> > +	BUG_ON(FIXADDR_TOP < (unsigned long)high_memory);
> > +#endif /* CONFIG_DEBUG_KERNEL */
> > +}
> > +#undef MLK
> > +#undef MLM
> > +#undef MLK_ROUNDUP
> > +
> >  /*
> >   * Not static inline because used by IP27 special magic initialization code
> >   */
> > @@ -479,6 +527,7 @@ void __init mem_init(void)
> >  	setup_zero_pages();	/* Setup zeroed pages.  */
> >  	mem_init_free_highmem();
> >  	mem_init_print_info(NULL);
> > +	mem_print_kmap_info();
> >  
> >  #ifdef CONFIG_64BIT
> >  	if ((unsigned long) &_text > (unsigned long) CKSEG0)
> > -- 
> > 2.21.0
> > 
> 
> -- 
> Sincerely yours,
> Mike.
>