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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

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Cc'ing firmware experts.

On 9/18/20 2:26 PM, haibinzhang(张海斌) 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
>