On Wed, Feb 07, 2018 at 06:37:16PM +0000, James Morse wrote: > Hi Akashi, > > On 04/12/17 02:57, AKASHI Takahiro wrote: > > This is a basic purgatory, or a kind of glue code between the two kernels, > > for arm64. > > > > Since purgatory is assumed to be relocatable (not executable) object by > > kexec generic code, arch_kexec_apply_relocations_add() is required in > > general. Arm64's purgatory, however, is a simple asm and all the references > > can be resolved as local, no re-linking is needed here. > > > > Please note that even if we don't support digest check at purgatory we > > (You knew what I was going to ask!) Yes, definitely. > > > need purgatory_sha_regions and purgatory_sha256_digest as they are > > referenced by generic kexec code. > > As somewhere to store the values? If we aren't doing the validation could we add > something about why not to the commit message? I think its because we only worry > about memory corruption for kdump, and for kdump we unmap the crash-kernel > region during normal-operation to prevent it getting corrupted. > > As we aren't doing the hash validation, could we hide its core-code behind some > ARCH_HAS_KEXEC_PURGATORY_HASH, instead of defining dummy symbols and doing > unnecessary work to fill them in? Yes, this is one idea. But as you mentioned below, adding a purgatory for arm64's kexec_file does make little sense as I've already removed digest check code after MarkR's comment. > > > diff --git a/arch/arm64/purgatory/entry.S b/arch/arm64/purgatory/entry.S > > new file mode 100644 > > index 000000000000..fe6e968076db > > --- /dev/null > > +++ b/arch/arm64/purgatory/entry.S > > @@ -0,0 +1,55 @@ > > +/* > > + * kexec core purgatory > > + */ > > +#include <linux/linkage.h> > > +#include <uapi/linux/kexec.h> > > + > > +#define SHA256_DIGEST_SIZE 32 /* defined in crypto/sha.h */ > > + > > +.text > > + > > +ENTRY(purgatory_start) > > + /* Start new image. */ > > + ldr x17, __kernel_entry > > + ldr x0, __dtb_addr > > + mov x1, xzr > > + mov x2, xzr > > + mov x3, xzr > > + br x17 > > +END(purgatory_start) > > Is this what arm64_relocate_new_kernel() drops into? I thought that had the > kernel boot register values already so we wouldn't need another trampoline for > kexec_file_load()... Indeed > .. but now that I look, it doesn't have the DTB, presumably because for regular > kexec we don't know where user-space put it. > > Could we add some x0_for_kexec that is 0 by default (if that's the ABI), or the First, I didn't get what you meaned here. After managing to modify my code, I found that we could re-use cpu_soft_restart(), especially, the fifth argument, which is currently contant 0, but we will be able to pass dtb address here. In turn, we can also use this argument to determine, in relocate_new_kernel(), whether we should call puragatory (kexec_load) or directly jump into the kernel (kexec_file_load). > DTB address for kexec_file_load()? This would avoid this extra trampoline, and > patching in the values from load_other_segments(). > > I'd love to avoid an in-kernel purgatory! (its code with funny > compile/link/relocation requirements that is impossible to debug) Lovely! I really appreicated your valuable comments. and more on other patches comming? -Takahiro AKASHI > > Thanks, > > James _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
