linux-kernel - Re: [Xen-devel] [PATCH 2/2] xen: before ballooning hotplugged memory, set frames to invalid

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Message-ID: <550B0536.2000104@suse.com>
Date:	Thu, 19 Mar 2015 18:19:50 +0100
From:	Juergen Gross <jgross@...e.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	daniel.kiper@...cle.com
Subject: Re: [Xen-devel] [PATCH 2/2] xen: before ballooning hotplugged memory,
 set frames to invalid

On 03/19/2015 05:18 PM, David Vrabel wrote:
> On 19/03/15 14:31, Juergen Gross wrote:
>> Commit 25b884a83d487fd62c3de7ac1ab5549979188482 ("x86/xen: set
>> regions above the end of RAM as 1:1") introduced a regression.
>>
>> To be able to add memory pages which were added via memory hotplug to
>> a pv domain, the pages must be "invalid" instead of "identity" in the
>> p2m list before they can be added.
> [...]
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -221,15 +221,24 @@ static bool balloon_is_inflated(void)
>>
>>   static enum bp_state reserve_additional_memory(long credit)
>>   {
>> -	int nid, rc;
>> +	int nid, rc = 0;
>>   	u64 hotplug_start_paddr;
>>   	unsigned long balloon_hotplug = credit;
>> +	unsigned long pfn;
>>
>>   	hotplug_start_paddr = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
>>   	balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
>>   	nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
>>
>> -	rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);
>> +	for (pfn = PFN_DOWN(hotplug_start_paddr);
>> +	     !rc && pfn < PFN_DOWN(hotplug_start_paddr) + balloon_hotplug;
>> +	     pfn++)
>> +		if (!set_phys_to_machine(pfn, INVALID_P2M_ENTRY))
>> +			rc = 1;
>
>      rc = -ENOMEM;

I used the value 1 on purpose to be able to identify the case by the
value printed in the warning below.

>      break;

Why? !rc is already tested in the for() clause.

>
>> +
>> +	if (!rc)
>> +		rc = add_memory(nid, hotplug_start_paddr,
>> +				balloon_hotplug << PAGE_SHIFT);
>
> Use else here.

Huh? I want the message to be printed if either set_phys_to_machine()
or add_memory() failed.

>
>>   	if (rc) {
>>   		pr_warn("Cannot add additional memory (%i)\n", rc);
>>


Juergen

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