Date:	Thu, 3 May 2012 17:27:27 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"JBeulich@...e.com" <JBeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH] auto balloon initial domain and fix dom0_mem=X
 inconsistencies (v5).

On 03/05/12 16:15, David Vrabel wrote:
> 
> xen: update VA mapping when releasing memory during setup
> 
> In xen_memory_setup(), if a page that is being released has a VA
> mapping this must also be updated.  Otherwise, the page will be not
> released completely -- it will still be referenced in Xen and won't be
> freed util the mapping is removed and this prevents it from being
> reallocated at a different PFN.
> 
> This was already being done for the ISA memory region in
> xen_ident_map_ISA() but on many systems this was omitting a few pages
> as many systems marked a few pages below the ISA memory region as
> reserved in the e820 map.
> 
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> ---
[...]
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1929,29 +1929,6 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
>  #endif
>  }
>  
> -void __init xen_ident_map_ISA(void)
> -{
> -	unsigned long pa;
> -
> -	/*
> -	 * If we're dom0, then linear map the ISA machine addresses into
> -	 * the kernel's address space.
> -	 */
> -	if (!xen_initial_domain())
> -		return;

It might look like this test has gone, however the new code which
updates the VA mapping uses the e820 map and for a domU its map will not
have a ISA region so there's no mapping to be updated.

David

> -
> -	xen_raw_printk("Xen: setup ISA identity maps\n");
> -
> -	for (pa = ISA_START_ADDRESS; pa < ISA_END_ADDRESS; pa += PAGE_SIZE) {
> -		pte_t pte = mfn_pte(PFN_DOWN(pa), PAGE_KERNEL_IO);
> -
> -		if (HYPERVISOR_update_va_mapping(PAGE_OFFSET + pa, pte, 0))
> -			BUG();
> -	}
> -
> -	xen_flush_tlb();
> -}
> -
>  static void __init xen_post_allocator_init(void)
>  {
>  	pv_mmu_ops.set_pte = xen_set_pte;
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 506a3e6..d5f8714 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -139,6 +139,13 @@ static unsigned long __init xen_do_chunk(unsigned long start,
>  
>  	return len;
>  }
> +
> +static unsigned long __init xen_release_chunk(unsigned long start,
> +					      unsigned long end)
> +{
> +	return xen_do_chunk(start, end, true);
> +}
> +
>  static unsigned long __init xen_populate_chunk(
>  	const struct e820entry *list, size_t map_size,
>  	unsigned long max_pfn, unsigned long *last_pfn,
> @@ -197,6 +204,29 @@ static unsigned long __init xen_populate_chunk(
>  	}
>  	return done;
>  }
> +
> +static void __init xen_set_identity_and_release_chunk(
> +	unsigned long start_pfn, unsigned long end_pfn, unsigned long nr_pages,
> +	unsigned long *released, unsigned long *identity)
> +{
> +	unsigned long pfn;
> +
> +	/*
> +	 * If the PFNs are currently mapped, the VA mapping also needs
> +	 * to be updated to be 1:1.
> +	 */
> +	for (pfn = start_pfn; pfn <= max_pfn_mapped && pfn < end_pfn; pfn++)
> +		(void)HYPERVISOR_update_va_mapping(
> +			(unsigned long)__va(pfn << PAGE_SHIFT),
> +			mfn_pte(pfn, PAGE_KERNEL_IO), 0);
> +
> +	if (start_pfn < nr_pages)
> +		*released += xen_release_chunk(
> +			start_pfn, min(end_pfn, nr_pages));
> +
> +	*identity += set_phys_range_identity(start_pfn, end_pfn);
> +}
> +
>  static unsigned long __init xen_set_identity_and_release(
>  	const struct e820entry *list, size_t map_size, unsigned long nr_pages)
>  {
> @@ -226,14 +256,11 @@ static unsigned long __init xen_set_identity_and_release(
>  			if (entry->type == E820_RAM)
>  				end_pfn = PFN_UP(entry->addr);
>  
> -			if (start_pfn < end_pfn) {
> -				if (start_pfn < nr_pages)
> -					released += xen_do_chunk(
> -						start_pfn, min(end_pfn, nr_pages), true);
> +			if (start_pfn < end_pfn)
> +				xen_set_identity_and_release_chunk(
> +					start_pfn, end_pfn, nr_pages,
> +					&released, &identity);
>  
> -				identity += set_phys_range_identity(
> -					start_pfn, end_pfn);
> -			}
>  			start = end;
>  		}
>  	}
> diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
> index b095739..506fa08 100644
> --- a/arch/x86/xen/xen-ops.h
> +++ b/arch/x86/xen/xen-ops.h
> @@ -28,7 +28,6 @@ void xen_setup_shared_info(void);
>  void xen_build_mfn_list_list(void);
>  void xen_setup_machphys_mapping(void);
>  pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn);
> -void xen_ident_map_ISA(void);
>  void xen_reserve_top(void);
>  extern unsigned long xen_max_p2m_pfn;
>  

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