Re: [PATCH] libxc: fix claim mode when creating HVM guest

[George Dunlap <george.dunlap@eu.citrix.com>]

On 01/29/2014 06:33 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, Jan 27, 2014 at 05:53:38PM +0000, Wei Liu wrote:
>> The original code is wrong because:
>> * claim mode wants to know the total number of pages needed while
>>    original code provides the additional number of pages needed.
>> * if pod is enabled memory will already be allocated by the time we try
>>    to claim memory.
>>
>> So the fix would be:
>> * move claim mode before actual memory allocation.
>> * pass the right number of pages to hypervisor.
>>
>> The "right number of pages" should be number of pages of target memory
>> minus VGA_HOLE_SIZE, regardless of whether PoD is enabled.
>>
>> This fixes bug #32.
>>
>> Signed-off-by: Wei Liu <wei.liu2@citrix.com>
>> Cc: Konrad Wilk <konrad.wilk@oracle.com>
>
> And also 'Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>'

Right, well nobody has shouted, so:

Release-acked-by: George Dunlap <george.dunlap@eu.citrix.com>

>
> Thank you!
>> Cc: George Dunlap <george.dunlap@eu.citrix.com>
>> Cc: Ian Campbell <ian.campbell@citrix.com>
>> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
>> ---
>> WRT 4.4 release: this patch should be accpeted, otherwise PoD + claim
>> mode is complete broken. If this patch is deemed too complicated, we
>> should flip the switch to disable claim mode by default for 4.4.
>> ---
>>   tools/libxc/xc_hvm_build_x86.c |   36 +++++++++++++++++++++++-------------
>>   1 file changed, 23 insertions(+), 13 deletions(-)
>>
>> diff --git a/tools/libxc/xc_hvm_build_x86.c b/tools/libxc/xc_hvm_build_x86.c
>> index 77bd365..dd3b522 100644
>> --- a/tools/libxc/xc_hvm_build_x86.c
>> +++ b/tools/libxc/xc_hvm_build_x86.c
>> @@ -49,6 +49,8 @@
>>   #define NR_SPECIAL_PAGES     8
>>   #define special_pfn(x) (0xff000u - NR_SPECIAL_PAGES + (x))
>>
>> +#define VGA_HOLE_SIZE (0x20)
>> +
>>   static int modules_init(struct xc_hvm_build_args *args,
>>                           uint64_t vend, struct elf_binary *elf,
>>                           uint64_t *mstart_out, uint64_t *mend_out)
>> @@ -302,14 +304,31 @@ static int setup_guest(xc_interface *xch,
>>       for ( i = mmio_start >> PAGE_SHIFT; i < nr_pages; i++ )
>>           page_array[i] += mmio_size >> PAGE_SHIFT;
>>
>> +    /*
>> +     * Try to claim pages for early warning of insufficient memory available.
>> +     * This should go before xc_domain_set_pod_target, becuase that function
>> +     * actually allocates memory for the guest. Claiming after memory has been
>> +     * allocated is pointless.
>> +     */
>> +    if ( claim_enabled ) {
>> +        rc = xc_domain_claim_pages(xch, dom, target_pages - VGA_HOLE_SIZE);
>> +        if ( rc != 0 )
>> +        {
>> +            PERROR("Could not allocate memory for HVM guest as we cannot claim memory!");
>> +            goto error_out;
>> +        }
>> +    }
>> +
>>       if ( pod_mode )
>>       {
>>           /*
>> -         * Subtract 0x20 from target_pages for the VGA "hole".  Xen will
>> -         * adjust the PoD cache size so that domain tot_pages will be
>> -         * target_pages - 0x20 after this call.
>> +         * Subtract VGA_HOLE_SIZE from target_pages for the VGA
>> +         * "hole".  Xen will adjust the PoD cache size so that domain
>> +         * tot_pages will be target_pages - VGA_HOLE_SIZE after
>> +         * this call.
>>            */
>> -        rc = xc_domain_set_pod_target(xch, dom, target_pages - 0x20,
>> +        rc = xc_domain_set_pod_target(xch, dom,
>> +                                      target_pages - VGA_HOLE_SIZE,
>>                                         NULL, NULL, NULL);
>>           if ( rc != 0 )
>>           {
>> @@ -333,15 +352,6 @@ static int setup_guest(xc_interface *xch,
>>       cur_pages = 0xc0;
>>       stat_normal_pages = 0xc0;
>>
>> -    /* try to claim pages for early warning of insufficient memory available */
>> -    if ( claim_enabled ) {
>> -        rc = xc_domain_claim_pages(xch, dom, nr_pages - cur_pages);
>> -        if ( rc != 0 )
>> -        {
>> -            PERROR("Could not allocate memory for HVM guest as we cannot claim memory!");
>> -            goto error_out;
>> -        }
>> -    }
>>       while ( (rc == 0) && (nr_pages > cur_pages) )
>>       {
>>           /* Clip count to maximum 1GB extent. */
>> --
>> 1.7.10.4
>>