Hi Peter, Sorry for the delay in replying to this...
On Thu, May 16, 2019 at 03:47:29PM +0100, Peter Maydell wrote: > > This patchset attempts to fix https://bugs.launchpad.net/qemu/+bug/1823998 > which reports that we don't handle kernels larger than 128MB > correctly, because we allow the initrd to be placed over the > tail end of the kernel. AArch64 kernel Image files (since v3.17) > report the total size they require (including any BSS area that > isn't in the Image itself), so we can use that to be sure we > place the initrd sufficiently far into the RAM. > > Patches 1 and 2 are new since v1; patches 3 and 4 are the old > patches 1 and 2 (and are basically unchanged since v1). > > Patches 1 and 2 in this series are new. Patch 1 fixes bugs > in the existing code where we were assuming that we could > treat info->ram_size as the address of the end of RAM, which > isn't true if the RAM doesn't start at address 0. (This > generally went unnoticed thanks to the magic of unsigned integer > underflow turning end-start calculations into very large max_size > values for load_ramdisk_as() and friends.) > Patch 2 adds some explicit checks that we don't try to put things > entirely off the end of RAM (which avoids those accidental > underflows). > Patch 3 in this series adjusts our "where do we put the initrd" > heuristic so that it always places it at least after whatever > our best guess at the kernel size is. (This might still not > be right for images like self-decompressing 32-bit kernels, where > there's no way to know how big the kernel will be after > decompression.) > Patch 4 makes load_aarch64_image() return the > kernel size as indicated in the Image file header, so that for > the specific case of AArch64 Image files we will definitely not > put the initrd on top of them. With all 4 patches applied, I'm able to boot kernels with large BSS segments (~128M, ~512M, and ~1G), and I get sensible warnings when they are impossible to boot, e.g. # 124M of RAM [mark@gravadlaks:~/repro]% ./vmboot.sh ~/Image.test-128M qemu-system-aarch64: kernel '/home/mark/Image.test-128M' is too large to fit in RAM (kernel size 155500544, RAM size 130023424) # 150M of RAM [mark@gravadlaks:~/repro]% ./vmboot.sh ~/Image.test-128M qemu-system-aarch64: Not enough space for DTB after kernel/initrd So feel free to add: Tested-by: Mark Rutland <mark.rutl...@arm.com> Thanks for putting this together; this is _really_ useful for my testing setup, and the warnings above are likely to save people a lot of head-scratching in future. It would be great to see this merged. :) Thanks, Mark.
