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Date: Tue, 12 Nov 2019 15:47:08 -0500
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 v4 4/4] x86/mm/KASLR: Adjust the padding size for the
direct mapping.
On Mon, Nov 04, 2019 at 08:48:25AM +0800, Baoquan He wrote:
> On 11/01/19 at 09:09pm, Masayoshi Mizuma wrote:
> > ---
> > arch/x86/mm/kaslr.c | 65 ++++++++++++++++++++++++++++++++++-----------
> > 1 file changed, 50 insertions(+), 15 deletions(-)
> >
> > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> > index dc6182eec..a80eed563 100644
> > --- a/arch/x86/mm/kaslr.c
> > +++ b/arch/x86/mm/kaslr.c
> > @@ -70,15 +70,60 @@ 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)
> > +{
> > + unsigned long padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
> > + unsigned long size_tb, memory_tb;
> > +#ifdef CONFIG_MEMORY_HOTPLUG
> > + unsigned long actual, maximum, base;
> > +
> > + if (boot_params.max_addr) {
> > + /*
> > + * The padding size should set to get for kaslr_regions[].base
> > + * bigger address than the maximum memory address the system can
> > + * have. kaslr_regions[].base points "actual size + padding" or
> > + * higher address. If "actual size + padding" points the lower
> > + * address than the maximum memory size, fix the padding size.
> > + */
> > + actual = roundup(PFN_PHYS(max_pfn), 1UL << TB_SHIFT);
> > + maximum = roundup(boot_params.max_addr, 1UL << TB_SHIFT);
> > + base = actual + (padding << TB_SHIFT);
> > +
> > + if (maximum > base)
> > + padding = (maximum - actual) >> TB_SHIFT;
> > + }
> > +#endif
> > + memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> > + padding;
>
> Yes, wrapping up the whole adjusting code block for the direct mapping
> area into a function looks much better. This was also suggested by Ingo
> when I posted UV system issue fix before, just later the UV system issue
> is not seen in the current code.
>
> However, I have a small concern about the memory_tb calculateion here.
> We can treat the (actual RAM + CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING)
> as the default memory_tb, then check if we need adjst it according to
> boot_params.max_addr. Discarding the local padding variable can make
> code much simpler? And it is a little confusing when mix with the
> later padding concept when doing randomization, I mean the get_padding()
> thing.
>
>
> memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
>
> if (boot_params.max_addr) {
> maximum = roundup(boot_params.max_addr, 1UL << TB_SHIFT);
>
> if (maximum > memory_tb)
> memory_tb = maximum;
> }
> #endif
>
> Personal opinion. Anyway, this patch looks good to me. Thanks.
Your suggesion makes it simpler, thanks!
So I'll modify calc_direct_mapping_size() as following.
Does it make sense?
static inline unsigned long calc_direct_mapping_size(void)
{
unsigned long size_tb, memory_tb;
memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
#ifdef CONFIG_MEMORY_HOTPLUG
if (boot_params.max_addr) {
unsigned long maximum_tb;
maximum_tb = DIV_ROUND_UP(boot_params.max_addr,
1UL << TB_SHIFT);
if (maximum_tb > memory_tb)
memory_tb = maximum_tb;
}
#endif
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;
}
Thanks,
Masa
>
> Thanks
> Baoquan
>
>
> > +
> > + 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 +140,10 @@ 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
> > --
> > 2.20.1
> >
>
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