Re: [PATCH v3 4/4] xen-all: Pass max_ram_below_4g to xen_hvm_init.

[Don Slutz <dslutz@verizon.com>]

On 04/18/14 12:19, Andreas Färber wrote:
> Am 25.03.2014 00:55, schrieb Don Slutz:
>> This is the xen part of "pc & q35: Add new object pc-memory-layout."
>>
>> Signed-off-by: Don Slutz <dslutz@verizon.com>
>> ---
>> v3: Adjust for code readability. Set max_ram_below_4g always and use
>> it to calculate above_4g_mem_size, below_4g_mem_size.
>>
>>   hw/i386/pc_piix.c    |  4 ++--
>>   hw/i386/pc_q35.c     |  4 ++--
>>   include/hw/xen/xen.h |  4 ++--
>>   xen-all.c            | 40 +++++++++++++++++++++-------------------
>>   xen-stub.c           |  4 ++--
>>   5 files changed, 29 insertions(+), 27 deletions(-)
>>
>> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
>> index 81d730d..8a93548 100644
>> --- a/hw/i386/pc_piix.c
>> +++ b/hw/i386/pc_piix.c
>> @@ -131,8 +131,8 @@ static void pc_init1(QEMUMachineInitArgs *args,
>>           below_4g_mem_size = args->ram_size;
>>       }
>>   
>> -    if (xen_enabled() && xen_hvm_init(&below_4g_mem_size, &above_4g_mem_size,
>> -                                      &ram_memory) != 0) {
>> +    if (xen_enabled() && xen_hvm_init(max_ram_below_4g, &below_4g_mem_size,
>> +                                      &above_4g_mem_size, &ram_memory) != 0) {
>>           fprintf(stderr, "xen hardware virtual machine initialisation failed\n");
>>           exit(1);
>>       }
>> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
>> index 529f53d..09e98e6 100644
>> --- a/hw/i386/pc_q35.c
>> +++ b/hw/i386/pc_q35.c
>> @@ -120,8 +120,8 @@ static void pc_q35_init(QEMUMachineInitArgs *args)
>>           below_4g_mem_size = args->ram_size;
>>       }
>>   
>> -    if (xen_enabled() && xen_hvm_init(&below_4g_mem_size, &above_4g_mem_size,
>> -                                      &ram_memory) != 0) {
>> +    if (xen_enabled() && xen_hvm_init(max_ram_below_4g, &below_4g_mem_size,
>> +                                      &above_4g_mem_size, &ram_memory) != 0) {
>>           fprintf(stderr, "xen hardware virtual machine initialisation failed\n");
>>           exit(1);
>>       }
>> diff --git a/include/hw/xen/xen.h b/include/hw/xen/xen.h
>> index 0f3942e..eca39a5 100644
>> --- a/include/hw/xen/xen.h
>> +++ b/include/hw/xen/xen.h
>> @@ -40,8 +40,8 @@ int xen_init(QEMUMachine *machine);
>>   void xenstore_store_pv_console_info(int i, struct CharDriverState *chr);
>>   
>>   #if defined(NEED_CPU_H) && !defined(CONFIG_USER_ONLY)
>> -int xen_hvm_init(ram_addr_t *below_4g_mem_size, ram_addr_t *above_4g_mem_size,
>> -                 MemoryRegion **ram_memory);
>> +int xen_hvm_init(ram_addr_t max_ram_below_4g, ram_addr_t *below_4g_mem_size,
>> +                 ram_addr_t *above_4g_mem_size, MemoryRegion **ram_memory);
>>   void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size,
>>                      struct MemoryRegion *mr);
>>   void xen_modified_memory(ram_addr_t start, ram_addr_t length);
>> diff --git a/xen-all.c b/xen-all.c
>> index c64300c..3f6f890 100644
>> --- a/xen-all.c
>> +++ b/xen-all.c
>> @@ -155,31 +155,32 @@ qemu_irq *xen_interrupt_controller_init(void)
>>   
>>   /* Memory Ops */
>>   
>> -static void xen_ram_init(ram_addr_t *below_4g_mem_size,
>> +static void xen_ram_init(ram_addr_t ram_size, ram_addr_t max_ram_below_4g,
>> +                         ram_addr_t *below_4g_mem_size,
>>                            ram_addr_t *above_4g_mem_size,
>> -                         ram_addr_t ram_size, MemoryRegion **ram_memory_p)
>> +                         MemoryRegion **ram_memory_p)
>>   {
>>       MemoryRegion *sysmem = get_system_memory();
>>       ram_addr_t block_len;
>>   
>> -    block_len = ram_size;
>> -    if (ram_size >= HVM_BELOW_4G_RAM_END) {
>> -        /* Xen does not allocate the memory continuously, and keep a hole at
>> -         * HVM_BELOW_4G_MMIO_START of HVM_BELOW_4G_MMIO_LENGTH
>> -         */
>> -        block_len += HVM_BELOW_4G_MMIO_LENGTH;
>> -    }
>> -    memory_region_init_ram(&ram_memory, NULL, "xen.ram", block_len);
>> -    *ram_memory_p = &ram_memory;
>> -    vmstate_register_ram_global(&ram_memory);
>> -
>> -    if (ram_size >= HVM_BELOW_4G_RAM_END) {
>> -        *above_4g_mem_size = ram_size - HVM_BELOW_4G_RAM_END;
>> -        *below_4g_mem_size = HVM_BELOW_4G_RAM_END;
>> +    max_ram_below_4g = max_ram_below_4g ? max_ram_below_4g : HVM_BELOW_4G_RAM_END;
> Isn't max_ram_below_4g still always zero at this point?

No. Patch 3/4 gets this from the global "max-ram-below-4g".  So
it is only 0 when the user has not set this.

> Are you guys still using your own Xen machine types?

Yes and no:

             flexarray_append(dm_args, "pc,accel=xen");
         } else {
             flexarray_append(dm_args, "xenfv");


>   Then you could set
> a compat_props entry for all (not just legacy) machines to override the
> actual pc-memory-layout max-ram-below-4g property value to avoid the ?:
> here. Especially since I'm not seeing this modified value being written
> back to the device.

I think this is still possible.  Will look into it.  Did not see any
need to write this back.


> Considering that machines are objects now, might it be easier to set
> this property on the machine object itself rather than having an unused
> stub object hanging in limbo?

That would be fine with me.

>   Would create a dependency on Marcel's
> series though (which like this series I now need to start reviewing).

I will look into using this machine object(s).  What I found was:


[PATCH v3 0/3] qemu-machine as a QOM object
[PATCH V3 0/5] remove QEMUMachine indirection from MachineClass

And if I have it correct, you are referring to the 2nd of these as
a dependency.



>> +    if (ram_size >= max_ram_below_4g) {
>> +        *above_4g_mem_size = ram_size - max_ram_below_4g;
>> +        *below_4g_mem_size = max_ram_below_4g;
>>       } else {
>>           *above_4g_mem_size = 0;
>>           *below_4g_mem_size = ram_size;
>>       }
>> +    if (!*above_4g_mem_size) {
>> +        block_len = ram_size;
>> +    } else {
>> +        /* Xen does not allocate the memory continuously, and keep a hole of
>> +         * of the size computed above or passed in. */
> Please keep */ in the front for easily spotting where the comment ends.
>
> Possibly even /* is requested to be on its own line by Coding Style...?
> But that'd be a mere code movement.
>

I did not find any statement about this in CODING_STYLE, but will adjust
to this.

    -Don Slutz

>> +        block_len = (1ULL << 32) + *above_4g_mem_size;
>> +    }
>> +    memory_region_init_ram(&ram_memory, NULL, "xen.ram", block_len);
>> +    *ram_memory_p = &ram_memory;
>> +    vmstate_register_ram_global(&ram_memory);
>>   
>>       memory_region_init_alias(&ram_640k, NULL, "xen.ram.640k",
>>                                &ram_memory, 0, 0xa0000);
> [snip]
>
> Regards,
> Andreas
>