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

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Date:	Thu, 09 Apr 2015 13:47:04 +0100
From:	David Vrabel <dvrabel@...tab.net>
To:	Juergen Gross <jgross@...e.com>, 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 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.

>  
>  /*
>   * 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.

> +void __init xen_pt_check_e820(void)
> +{
> +	if (xen_chk_e820_reserved(xen_pt_base, xen_pt_size)) {
> +		xen_raw_console_write("Xen hypervisor allocated page table memory conflicts with E820 map\n");
> +		BUG();
> +	}
> +}
> +
>  static unsigned char dummy_mapping[PAGE_SIZE] __page_aligned_bss;

David
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