Hi Peter, Thanks for your reply!
On 2019/3/25 21:11, Peter Maydell wrote: > On Mon, 25 Mar 2019 at 12:53, Xiang Zheng <zhengxia...@huawei.com> wrote: >> >> Currently we fill the VIRT_FLASH space with two 64MB NOR images when >> using persistent UEFI variables on QEMU. Actually we only use a very >> small part of the memory while the rest significant large part of >> memory is wasted. >> >> This patch creates and maps a variable size of flash device instead of >> a mandatory 64MB one to save memory. >> >> Signed-off-by: Xiang Zheng <zhengxia...@huawei.com> >> --- >> >> This patch might be insufficient since it also needs to modify the flash size >> in ACPI and DTB. >> >> BTW, I don't understand why it requires the two NOR images to be exactly 64MB >> in size when using -pflash. > > I don't think we should do this. The board should in general > create the same hardware visible to the guest, not change > it based on subtle things like the size of the image files. > > The reason why the flash images must be 64MB in size > when using -pflash is that they are the backing store > for a writable device. Suppose you have 1MB of data in your > backing image that you pass to QEMU and then the guest writes > to the last block of the flash device. The new data > written by the guest to the end of the device has to be > stored somewhere, so the file has to be large enough > to cover the whole of the flash area. > Is there any way to support config or limit the size that both guest and QEMU are visible? The original QEMU_EFI.fd has only 2M, but we need to stuff it to 64M with 62M unused data. It will consume a large amount of memory when running multiple VM simultaneously. -- Thanks, Xiang
