linux-kernel - Re: [PATCH v3 4/5] x86/mm/KASLR: Cleanup calculation for direct mapping size

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Date:   Tue, 29 Oct 2019 11:55:39 -0400
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/5] x86/mm/KASLR: Cleanup calculation for direct
 mapping size

On Thu, Sep 05, 2019 at 09:54:51PM +0800, Baoquan He wrote:
> On 08/30/19 at 05:47pm, Masayoshi Mizuma wrote:
> > From: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
> > 
> > Cleanup calculation for direct mapping size.
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > Signed-off-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
> > ---
> >  arch/x86/mm/kaslr.c | 50 +++++++++++++++++++++++++++++++--------------
> >  1 file changed, 35 insertions(+), 15 deletions(-)
> > 
> > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> > index dc6182eec..8e5f3642e 100644
> > --- a/arch/x86/mm/kaslr.c
> > +++ b/arch/x86/mm/kaslr.c
> > @@ -70,15 +70,45 @@ static inline bool kaslr_memory_enabled(void)
> >  	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
> >  }
> >  
> > +/*
> > + * Even though a huge virtual address space is reserved for the direct
> > + * mapping of physical memory, e.g in 4-level paging mode, it's 64TB,
> > + * rare system can own enough physical memory to use it up, most are
> > + * even less than 1TB. So with KASLR enabled, we adapt the size of
> > + * direct mapping area to the size of actual physical memory plus the
> > + * configured padding CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING.
> > + * The left part will be taken out to join memory randomization.
> > + */
> > +static inline unsigned long calc_direct_mapping_size(void)
> 
> I think patch 4 and 5 can be merged, just keep one
> calc_direct_mapping_size() to do the mapping size calculation for the
> direct mapping section, it's not that complicated. Adding
> phys_memmap_size() makes it a little redundent, in my opinion.

Thanks, I'll merge patch 4 and 5.

- Masa

> 
> Thanks
> Baoquan
> 
> > +{
> > +	unsigned long size_tb, memory_tb;
> > +
> > +	/*
> > +	 * Update Physical memory mapping to available and
> > +	 * add padding if needed (especially for memory hotplug support).
> > +	 */
> > +	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> > +		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
> > +
> > +	size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
> > +
> > +	/*
> > +	 * Adapt physical memory region size based on available memory
> > +	 */
> > +	if (memory_tb < size_tb)
> > +		size_tb = memory_tb;
> > +
> > +	return size_tb;
> > +}
> > +
> >  /* Initialize base and padding for each memory region randomized with KASLR */
> >  void __init kernel_randomize_memory(void)
> >  {
> > -	size_t i;
> > -	unsigned long vaddr_start, vaddr;
> > -	unsigned long rand, memory_tb;
> > -	struct rnd_state rand_state;
> > +	unsigned long vaddr_start, vaddr, rand;
> >  	unsigned long remain_entropy;
> >  	unsigned long vmemmap_size;
> > +	struct rnd_state rand_state;
> > +	size_t i;
> >  
> >  	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
> >  	vaddr = vaddr_start;
> > @@ -95,20 +125,10 @@ void __init kernel_randomize_memory(void)
> >  	if (!kaslr_memory_enabled())
> >  		return;
> >  
> > -	kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
> > +	kaslr_regions[0].size_tb = calc_direct_mapping_size();
> >  	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
> >  
> > -	/*
> > -	 * Update Physical memory mapping to available and
> > -	 * add padding if needed (especially for memory hotplug support).
> > -	 */
> >  	BUG_ON(kaslr_regions[0].base != &page_offset_base);
> > -	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> > -		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
> > -
> > -	/* Adapt phyiscal memory region size based on available memory */
> > -	if (memory_tb < kaslr_regions[0].size_tb)
> > -		kaslr_regions[0].size_tb = memory_tb;
> >  
> >  	/*
> >  	 * Calculate the vmemmap region size in TBs, aligned to a TB
> > -- 
> > 2.18.1
> >