linux-kernel - Re: [Xen-devel] [Patch V2 10/15] xen: check pre-allocated page tables for conflict with memory map

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Message-ID: <552679EE.1020704@suse.com>
Date:	Thu, 09 Apr 2015 15:09:02 +0200
From:	Juergen Gross <jgross@...e.com>
To:	David Vrabel <dvrabel@...tab.net>, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com, konrad.wilk@...cle.com,
	david.vrabel@...rix.com, boris.ostrovsky@...cle.com,
	linux-mm@...ck.org
Subject: Re: [Xen-devel] [Patch V2 10/15] xen: check pre-allocated page tables
 for conflict with memory map

On 04/09/2015 02:47 PM, David Vrabel wrote:
> On 09/04/2015 07:55, Juergen Gross wrote:
>> Check whether the page tables built by the domain builder are at
>> memory addresses which are in conflict with the target memory map.
>> If this is the case just panic instead of running into problems
>> later.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   arch/x86/xen/mmu.c     | 19 ++++++++++++++++---
>>   arch/x86/xen/setup.c   |  6 ++++++
>>   arch/x86/xen/xen-ops.h |  1 +
>>   3 files changed, 23 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
>> index 1ca5197..41aeb1c 100644
>> --- a/arch/x86/xen/mmu.c
>> +++ b/arch/x86/xen/mmu.c
>> @@ -116,6 +116,7 @@ static pud_t level3_user_vsyscall[PTRS_PER_PUD] __page_aligned_bss;
>>   DEFINE_PER_CPU(unsigned long, xen_cr3);	 /* cr3 stored as physaddr */
>>   DEFINE_PER_CPU(unsigned long, xen_current_cr3);	 /* actual vcpu cr3 */
>>
>> +static phys_addr_t xen_pt_base, xen_pt_size;
>
> These be __init, but the use of globals in this way is confusing.

How else would you want to do it?

>
>>
>>   /*
>>    * Just beyond the highest usermode address.  STACK_TOP_MAX has a
>> @@ -1998,7 +1999,9 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
>>   		check_pt_base(&pt_base, &pt_end, addr[i]);
>>
>>   	/* Our (by three pages) smaller Xen pagetable that we are using */
>> -	memblock_reserve(PFN_PHYS(pt_base), (pt_end - pt_base) * PAGE_SIZE);
>> +	xen_pt_base = PFN_PHYS(pt_base);
>> +	xen_pt_size = (pt_end - pt_base) * PAGE_SIZE;
>> +	memblock_reserve(xen_pt_base, xen_pt_size);
>
> Why not provide a xen_memblock_check_and_reserve() call that has the
> xen_is_e820_reserved() check and the memblock_reserve() call?  This may
> also be useful for patch #9 as well.

Uuh, not really. memblock_reserve() for those areas is called much
earlier than the e820 map is constructed.

Thinking more about it, I even have to modify patch 11 and 13:
relocation must be done _after_ doing the memblock_reserve() of all
pre-populated areas to avoid relocating to such an area.


Juergen

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