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

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Message-ID: <550B05BE.7060102@suse.com>
Date:	Thu, 19 Mar 2015 18:22:06 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Daniel Kiper <daniel.kiper@...cle.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, david.vrabel@...rix.com,
	boris.ostrovsky@...cle.com
Subject: Re: [PATCH 2/2] xen: before ballooning hotplugged memory, set frames
 to invalid

On 03/19/2015 05:21 PM, Daniel Kiper wrote:
> On Thu, Mar 19, 2015 at 03:31:02PM +0100, 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.
>>
>> Suggested-by: David Vrabel <david.vrabel@...rix.com>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   drivers/xen/balloon.c | 13 +++++++++++--
>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index 0b52d92..52e331f 100644
>> --- 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 = set_phys_to_machine(pfn, INVALID_P2M_ENTRY)?

Not really. set_phys_to_machine returns false on failure...

>
>> +			rc = 1;
>
> I do not think that this stuff is needed for HVM or PVH guests.

True.

>
>> +	if (!rc)
>> +		rc = add_memory(nid, hotplug_start_paddr,
>> +				balloon_hotplug << PAGE_SHIFT);
>>
>>   	if (rc) {
>>   		pr_warn("Cannot add additional memory (%i)\n", rc);
>
> It will be nice to know what part of infrastructure failed.
> Could you create separate pr_warn() message for set_phys_to_machine()?

Value 1 for rc is the indicator for that case.


Juergen
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