Re: [Qemu-devel] [PATCH v2 4/4] xen-all: Pass max_ram_below_4g to xen_hvm_init.

[Don Slutz <dslutz@verizon.com>]

On 03/16/14 12:10, Stefano Stabellini wrote:
> On Tue, 11 Mar 2014, Don Slutz wrote:
>> This is the xen part of "pc & q35: Add new object pc-memory-layout."
>>
>> Signed-off-by: Don Slutz<dslutz@verizon.com>
>> ---
>>   hw/i386/pc_piix.c    |  4 ++--
>>   hw/i386/pc_q35.c     |  4 ++--
>>   include/hw/xen/xen.h |  4 ++--
>>   xen-all.c            | 41 ++++++++++++++++++++++-------------------
>>   xen-stub.c           |  4 ++--
>>   5 files changed, 30 insertions(+), 27 deletions(-)
>>
>> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
>> index 964ea33..691fc5d 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 c95e6e2..8e1c417 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 0769db2..fda559a 100644
>> --- a/include/hw/xen/xen.h
>> +++ b/include/hw/xen/xen.h
>> @@ -41,8 +41,8 @@ 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..48ba335 100644
>> --- a/xen-all.c
>> +++ b/xen-all.c
>> @@ -155,32 +155,34 @@ 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;
>> +    if (!max_ram_below_4g) {
>> +        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;
>> +        } else {
>> +            *above_4g_mem_size = 0;
>> +            *below_4g_mem_size = ram_size;
>> +        }
>> +    }
> Instead of treating max_ram_below_4g as a special case, couldn't
> initialize it to HVM_BELOW_4G_RAM_END?

Since max_ram_below_4g is used and initialize in normal QEMU code
where HVM_BELOW_4G_RAM_END is not defined, I do not see how to
do this outside of this routine without adding a new routine for this.

> We could consider HVM_BELOW_4G_RAM_END as the upper bound of
> max_ram_below_4g.

Yes.  Currently the only limit on max_ram_below_4g is 4G.  I am on
the fence on this.  I think there are valid values > HVM_BELOW_4G_RAM_END,
but not clear they need to be supported.

> I would just change the code to:
>
>      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 {
>          below_4g_mem_size = ram_size;
>      }
>

This is the code that is in patch #3 in the normal QEMU path but using
the variable lowmem so that xen can know if max_ram_below_4g was
set to non-zero.  The issue that I am looking at handling here is the case
of an older xen (does not know about  max_ram_below_4g) and the
newer QEMU, where xen expects QEMUs memory layout to change to
HVM_BELOW_4G_RAM_END.

Because of this (QEMU is doing the right thing if max_ram_below_4g is
non-zero) is why I coded it as only when max_ram_below_4g is zero, the
xen default is not the same as QEMU.

    -Don Slutz


>> +    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. */
>> +        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);
>>   
>> -    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;
>> -    } else {
>> -        *above_4g_mem_size = 0;
>> -        *below_4g_mem_size = ram_size;
>> -    }
>> -
>>       memory_region_init_alias(&ram_640k, NULL, "xen.ram.640k",
>>                                &ram_memory, 0, 0xa0000);
>>       memory_region_add_subregion(sysmem, 0, &ram_640k);
>> @@ -1069,8 +1071,8 @@ static void xen_wakeup_notifier(Notifier *notifier, void *data)
>>       xc_set_hvm_param(xen_xc, xen_domid, HVM_PARAM_ACPI_S_STATE, 0);
>>   }
>>   
>> -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)
>>   {
>>       int i, rc;
>>       unsigned long ioreq_pfn;
>> @@ -1148,7 +1150,8 @@ int xen_hvm_init(ram_addr_t *below_4g_mem_size, ram_addr_t *above_4g_mem_size,
>>   
>>       /* Init RAM management */
>>       xen_map_cache_init(xen_phys_offset_to_gaddr, state);
>> -    xen_ram_init(below_4g_mem_size, above_4g_mem_size, ram_size, ram_memory);
>> +    xen_ram_init(ram_size, max_ram_below_4g, below_4g_mem_size,
>> +                 above_4g_mem_size, ram_memory);
>>   
>>       qemu_add_vm_change_state_handler(xen_hvm_change_state_handler, state);
>>   
>> diff --git a/xen-stub.c b/xen-stub.c
>> index 0302dff..dd317a5 100644
>> --- a/xen-stub.c
>> +++ b/xen-stub.c
>> @@ -64,8 +64,8 @@ void xen_modified_memory(ram_addr_t start, ram_addr_t length)
>>   {
>>   }
>>   
>> -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)
>>   {
>>       return 0;
>>   }
>> -- 
>> 1.8.4
>>