linux-kernel - Re: [PATCH V3 4/8] xen: Delay invalidating extra memory

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Date:	Thu, 13 Nov 2014 07:49:24 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	david.vrabel@...rix.com, boris.ostrovsky@...cle.com,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH V3 4/8] xen: Delay invalidating extra memory

On 11/12/2014 11:10 PM, Konrad Rzeszutek Wilk wrote:
>> @@ -376,12 +374,14 @@ void __init xen_build_dynamic_phys_to_machine(void)
>>   	unsigned long max_pfn;
>>   	unsigned long pfn;
>>
>> -	 if (xen_feature(XENFEAT_auto_translated_physmap))
>> +	if (xen_feature(XENFEAT_auto_translated_physmap))
>
> Spurious change.

I'll remove it.

>
> .. snip..
>> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
>> index 0e5f9b6..8d5985b 100644
>> --- a/arch/x86/xen/setup.c
>> +++ b/arch/x86/xen/setup.c
>> @@ -75,7 +75,6 @@ static unsigned long xen_remap_mfn __initdata = INVALID_P2M_ENTRY;
>>
>>   static void __init xen_add_extra_mem(u64 start, u64 size)
>>   {
>> -	unsigned long pfn;
>>   	int i;
>>
>>   	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
>> @@ -95,17 +94,74 @@ static void __init xen_add_extra_mem(u64 start, u64 size)
>>   		printk(KERN_WARNING "Warning: not enough extra memory regions\n");
>>
>>   	memblock_reserve(start, size);
>> +}
>>
>> -	xen_max_p2m_pfn = PFN_DOWN(start + size);
>> -	for (pfn = PFN_DOWN(start); pfn < xen_max_p2m_pfn; pfn++) {
>> -		unsigned long mfn = pfn_to_mfn(pfn);
>> +static void __init xen_del_extra_mem(u64 start, u64 size)
>> +{
>> +	int i;
>> +	u64 start_r, size_r;
>>
>> -		if (WARN_ONCE(mfn == pfn, "Trying to over-write 1-1 mapping (pfn: %lx)\n", pfn))
>> -			continue;
>> -		WARN_ONCE(mfn != INVALID_P2M_ENTRY, "Trying to remove %lx which has %lx mfn!\n",
>> -			  pfn, mfn);
>> +	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
>> +		start_r = xen_extra_mem[i].start;
>> +		size_r = xen_extra_mem[i].size;
>> +
>> +		/* Start of region. */
>> +		if (start_r == start) {
>> +			BUG_ON(size > size_r);
>> +			xen_extra_mem[i].start += size;
>> +			xen_extra_mem[i].size -= size;
>> +			break;
>> +		}
>> +		/* End of region. */
>> +		if (start_r + size_r == start + size) {
>> +			BUG_ON(size > size_r);
>> +			xen_extra_mem[i].size -= size;
>> +			break;
>> +		}
>> +		/* Mid of region. */
>> +		if (start > start_r && start < start_r + size_r) {
>> +			BUG_ON(start + size > start_r + size_r);
>> +			xen_extra_mem[i].size = start - start_r;
>> +			xen_add_extra_mem(start + size, start_r + size_r -
>> +					  (start + size));
>
> Which ends up calling 'memblock_reserve' for an region it already has
> reserved. Should we call memblock_free(start_r, size_r - size) before calling this?
>
> Or is that not neccessary as memblock_* is pretty smart about this sort of thing?

Regions marked via memblock_reserve() are allowed to overlap. I can add
a comment.


Juergen

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