Messages in this thread | | | Date | Tue, 27 Jan 2015 09:24:59 -0500 | From | Vivek Goyal <> | Subject | Re: Edited kexec_load(2) [kexec_file_load()] man page for review |
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On Fri, Jan 16, 2015 at 02:30:25PM +0100, Michael Kerrisk (man-pages) wrote: [..] >
Hi Michael,
Please find my responses below. Sorry, I got stuck in other work and forgot about this thread.
> So, returning to the kexeec_segment structure: > > struct kexec_segment { > void *buf; /* Buffer in user space */ > size_t bufsz; /* Buffer length in user space */ > void *mem; /* Physical address of kernel */ > size_t memsz; /* Physical address length */ > }; > > Are the following statements correct: > * buf + bufsz identify a memory region in the caller's virtual > address space that is the source of the copy
Yes.
> * mem + memsz specify the target memory region of the copy
Yes.
> * mem is physical memory address, as seen from kernel space
Yes.
> * the number of bytes copied from userspace is min(bufsz, memsz)
Yes. bufsz can not be more than memsz. There is a check to validate this in kernel.
result = -EINVAL; for (i = 0; i < nr_segments; i++) { if (image->segment[i].bufsz > image->segment[i].memsz) return result; }
> * if bufsz > memsz, then excess bytes in the user-space buffer > are ignored.
You will get -EINVAL.
> * if memsz > bufsz, then excess bytes in the target kernel buffer > are filled with zeros.
Yes.
> Also, it seems to me that 'mem' need not be page aligned. > Is that correct? Should the man page say something about that? > (E.g., is it generally desirable that 'mem' should be page aligned?)
mem and memsz need to be page aligned. There is a check for that too.
mstart = image->segment[i].mem; mend = mstart + image->segment[i].memsz; if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK)) return result;
> > Likewise, 'memsz' doesn't need to beta page multiple, IIUC. > Should the man page say anything about this? For example, should > it note that the initialized kernel segment will be of size: > > (mem % PAGE_SIZE + memsz) rounded up to the next multiple of PAGE_SIZE > > And should it note that if 'mem' is not a multiple of the page size, then > the initial bytes (mem % PAGE_SIZE)) in the first page of the kernel segment > will be zeros? > > (Hopefully I have read kimage_load_normal_segment() correctly.)
Both mem and memsz need to be page aligned.
> > And one further question. Other than the fact that they are used with > different system calls, what is the difference between KEXEC_ON_CRASH > and KEXEC_FILE_ON_CRASH?
Right now I can't think of any other difference. They both tell respective system call that this kernel needs to be loaded in reserved memory region for crash kernel.
Thanks Vivek
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