On Thu, Sep 26, 2019 at 1:36 AM Kairui Song <kasong@xxxxxxxxxx> wrote: > > On Wed, Sep 25, 2019 at 11:25 PM Ard Biesheuvel > <ard.biesheuvel@xxxxxxxxxx> wrote: > > > > On Thu, 19 Sep 2019 at 18:06, Kairui Song <kasong@xxxxxxxxxx> wrote: > > > > > > Currently, kernel fails to boot on some HyperV VMs when using EFI. > > > And it's a potential issue on all platforms. > > > > > > It's caused a broken kernel relocation on EFI systems, when below three > > > conditions are met: > > > > > > 1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR) > > > by the loader. > > > 2. There isn't enough room to contain the kernel, starting from the > > > default load address (eg. something else occupied part the region). > > > 3. In the memmap provided by EFI firmware, there is a memory region > > > starts below LOAD_PHYSICAL_ADDR, and suitable for containing the > > > kernel. > > > > > > Efi stub will perform a kernel relocation when condition 1 is met. But > > > due to condition 2, efi stub can't relocate kernel to the preferred > > > address, so it fallback to query and alloc from EFI firmware for lowest > > > usable memory region. > > > > > > It's incorrect to use the lowest memory address. In later stage, kernel > > > will assume LOAD_PHYSICAL_ADDR as the minimal acceptable relocate address, > > > but efi stub will end up relocating kernel below it. > > > > > > Then before the kernel decompressing. Kernel will do another relocation > > > to address not lower than LOAD_PHYSICAL_ADDR, this time the relocate will > > > over write the blockage at the default load address, which efi stub tried > > > to avoid, and lead to unexpected behavior. Beside, the memory region it > > > writes to is not allocated from EFI firmware, which is also wrong. > > > > > > To fix it, just don't let efi stub relocate the kernel to any address > > > lower than lowest acceptable address. > > > > > > Signed-off-by: Kairui Song <kasong@xxxxxxxxxx> > > > > > > > Hello Kairui, > > > > This patch looks correct to me, but it needs an ack from the x86 > > maintainers, since the rules around LOAD_PHYSICAL_ADDR are specific to > > the x86 architecture. > > > > > > Thanks for the review, Ard. > > Can any x86 maintainer help provide some review? > > -- > Best Regards, > Kairui Song Ping? Any comments? -- Best Regards, Kairui Song
