Re: [PATCH] hw/arm/virt: use pflash image real size when mapping

[Laszlo Ersek <lersek@redhat.com>]

On 09/18/20 15:41, Philippe Mathieu-Daudé wrote:
> Cc'ing firmware experts.
> 
> On 9/18/20 2:26 PM, haibinzhang(寮犳捣鏂�) wrote:
>> Default size of arm-virt pflash image is 64MB which
>> will cost extra 128MB(64MBx2) memory per qemu process
>> and 12.5GB for 100 qemu processes. Host memory is
>> precious and it is valuable to reduce pflash image size.
>> For compatibility arm-virt uses real size when mapping.
> 
> Flash#0 is a device because eventually its model will handle
> sector/block protection, so firmware can do CapsuleUpdate
> (updating itself). Meanwhile you could treat flash#0 as a pure
> ROM device... But this wouldn't be the 'arm-virt' machine anymore.
> 
>>
>> Signed-off-by: Haibin Zhang <haibinzhang@tencent.com>
>> ---
>>  hw/arm/virt.c | 22 ++++++++++++++++++++--
>>  1 file changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
>> index acf9bfbece..3545e12865 100644
>> --- a/hw/arm/virt.c
>> +++ b/hw/arm/virt.c
>> @@ -50,6 +50,7 @@
>>  #include "sysemu/sysemu.h"
>>  #include "sysemu/tpm.h"
>>  #include "sysemu/kvm.h"
>> +#include "sysemu/block-backend.h"
>>  #include "hw/loader.h"
>>  #include "exec/address-spaces.h"
>>  #include "qemu/bitops.h"
>> @@ -1001,10 +1002,27 @@ static void virt_flash_map(VirtMachineState *vms,
>>       */
>>      hwaddr flashsize = vms->memmap[VIRT_FLASH].size / 2;
>>      hwaddr flashbase = vms->memmap[VIRT_FLASH].base;
>> +    int64_t realsize;
>> +    BlockBackend *blk;
>>
>> -    virt_flash_map1(vms->flash[0], flashbase, flashsize,
>> +    realsize = flashsize;
>> +    blk = pflash_cfi01_get_blk(vms->flash[0]);
>> +    if (blk) {
>> +        realsize = blk_getlength(blk);
>> +        realsize = realsize < flashsize ? realsize : flashsize;
>> +    }
> 
> Stefan recently posted "nvdimm: read-only file support" which
> might be a better way to achieve what you want:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg741137.html
> 
>> +
>> +    virt_flash_map1(vms->flash[0], flashbase, realsize,
>>                      secure_sysmem);
>> -    virt_flash_map1(vms->flash[1], flashbase + flashsize, flashsize,
>> +
>> +    realsize = flashsize;
>> +    blk = pflash_cfi01_get_blk(vms->flash[1]);
>> +    if (blk) {
>> +        realsize = blk_getlength(blk);
>> +        realsize = realsize < flashsize ? realsize : flashsize;
>> +    }
>> +
>> +    virt_flash_map1(vms->flash[1], flashbase + flashsize, realsize,
>>                      sysmem);
>>  }
>>
>> --
>> 2.23.0
>>
> 

We've been here before.

  [Qemu-devel] [RFC PATCH] hw/arm/virt: use variable size of flash device to save memory

  https://lists.gnu.org/archive/html/qemu-devel/2019-03/msg06773.html
  http://mid.mail-archive.com/20190325125142.11628-1-zhengxiang9@huawei.com

I don't have anything to add.

Laszlo