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Message-ID: <20100327000723.GF29222@cmpxchg.org>
Date: Sat, 27 Mar 2010 01:07:23 +0100
From: Johannes Weiner <hannes@...xchg.org>
To: Yinghai Lu <yinghai@...nel.org>
Cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
David Miller <davem@...emloft.net>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 02/24] x86: Make sure free_init_pages() free pages in boundary
On Fri, Mar 26, 2010 at 04:45:56PM -0700, Yinghai Lu wrote:
> On 03/26/2010 04:06 PM, Johannes Weiner wrote:
> > On Fri, Mar 26, 2010 at 03:21:32PM -0700, Yinghai Lu wrote:
> >> diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
> >> index adedeef..fe3d953 100644
> >> --- a/arch/x86/kernel/head32.c
> >> +++ b/arch/x86/kernel/head32.c
> >> @@ -47,6 +47,7 @@ void __init i386_start_kernel(void)
> >> u64 ramdisk_image = boot_params.hdr.ramdisk_image;
> >> u64 ramdisk_size = boot_params.hdr.ramdisk_size;
> >> u64 ramdisk_end = ramdisk_image + ramdisk_size;
> >> + ramdisk_end = PFN_UP(ramdisk_end) << PAGE_SHIFT;
> >
> > Why not PAGE_ALIGN()?
>
> looks like PFN_UP is more clear.
Why would you convert to a pfn just to go back to a physical address,
when all you wanted is align at the next page boundary? It looks
rather clumsy.
PAGE_ALIGN() is pretty wide spread and I think it's clear to most
people what it does.
> >> + size_aligned = ramdisk_end - ramdisk_image;
> >> +
> >> /* We need to move the initrd down into lowmem */
> >> - ramdisk_here = find_e820_area(0, end_of_lowmem, ramdisk_size,
> >> + ramdisk_here = find_e820_area(0, end_of_lowmem, size_aligned,
> >> PAGE_SIZE);
> >>
> >> if (ramdisk_here == -1ULL)
> >> panic("Cannot find place for new RAMDISK of size %lld\n",
> >> - ramdisk_size);
> >> + size_aligned);
> >>
> >> /* Note: this includes all the lowmem currently occupied by
> >> the initrd, we rely on that fact to keep the data intact. */
> >> - reserve_early(ramdisk_here, ramdisk_here + ramdisk_size,
> >> + reserve_early(ramdisk_here, ramdisk_here + size_aligned,
> >> "NEW RAMDISK");
> >> initrd_start = ramdisk_here + PAGE_OFFSET;
> >> initrd_end = initrd_start + ramdisk_size;
> >> printk(KERN_INFO "Allocated new RAMDISK: %08llx - %08llx\n",
> >> - ramdisk_here, ramdisk_here + ramdisk_size);
> >> + ramdisk_here, ramdisk_here + size_aligned);
> >>
> >> q = (char *)initrd_start;
> >>
> >> /* Copy any lowmem portion of the initrd */
> >> - if (ramdisk_image < end_of_lowmem) {
> >> - clen = end_of_lowmem - ramdisk_image;
> >> - p = (char *)__va(ramdisk_image);
> >> + image = ramdisk_image;
> >> + if (image < end_of_lowmem) {
> >> + clen = end_of_lowmem - image;
> >> + p = (char *)__va(image);
> >> memcpy(q, p, clen);
> >> q += clen;
> >> - ramdisk_image += clen;
> >> - ramdisk_size -= clen;
> >> + image += clen;
> >> + size_aligned -= clen;
> >> }
> >>
> >> /* Copy the highmem portion of the initrd */
> >> - while (ramdisk_size) {
> >> - slop = ramdisk_image & ~PAGE_MASK;
> >> - clen = ramdisk_size;
> >> + while (size_aligned) {
> >> + slop = image & ~PAGE_MASK;
> >> + clen = size_aligned;
> >> if (clen > MAX_MAP_CHUNK-slop)
> >> clen = MAX_MAP_CHUNK-slop;
> >> - mapaddr = ramdisk_image & PAGE_MASK;
> >> + mapaddr = image & PAGE_MASK;
> >> p = early_memremap(mapaddr, clen+slop);
> >> memcpy(q, p+slop, clen);
> >> early_iounmap(p, clen+slop);
> >> q += clen;
> >> - ramdisk_image += clen;
> >> - ramdisk_size -= clen;
> >> + image += clen;
> >> + size_aligned -= clen;
> >
> > Those appear to be a lot of spurious changes. We don't need to
> > copy the alignment padding as well, so it only matters that the
> > arguments to find_e820_area() and reserve_early() are aligned, no?
>
> we need to reserve that whole page, otherwise other user may use the same page.
I know that. And you would know that I know that, if you actually
read what I wrote.
> >> --- a/arch/x86/mm/init.c
> >> +++ b/arch/x86/mm/init.c
> >> @@ -332,6 +332,16 @@ int devmem_is_allowed(unsigned long pagenr)
> >> void free_init_pages(char *what, unsigned long begin, unsigned long end)
> >> {
> >> unsigned long addr = begin;
> >> + unsigned long addr_aligned, end_aligned;
> >> +
> >> + /* Make sure boundaries are page aligned */
> >> + addr_aligned = PFN_UP(addr) << PAGE_SHIFT;
> >> + end_aligned = PFN_DOWN(end) << PAGE_SHIFT;
> >> +
> >> + if (WARN(addr_aligned != addr || end_aligned != end, "free_init_pages: range [%#lx, %#lx] is not aligned\n", addr, end)) {
> >> + addr = addr_aligned;
> >> + end = end_aligned;
> >> + }
> >
> > Maybe realign only for when it is not aligned? So to keep the fixup
> > out of line.
> >
> > I suppose WARN_ON() is enough as it will print a stack trace which
> > should be enough clue of what went wrong.
>
> we need to PFN_DOWN the end, and don't free the partial page.
> otherwise could crash the system.
Dito.
if (WARN_ON(not_aligned)) {
align
}
is what I meant.
> So just print out the trace, and system still can be used. reporter to get dmesg if
> he don't have serial console.
/me goes arguing with M-x doctor, that thing actually acts on the
supplied input.
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