From: Masami Hiramatsu <mhiramat@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
systemtap-ml <systemtap@sources.redhat.com>
Subject: Re: [BUGFIX][PATCH -tip] x86: fix text_poke to handle highmem pages
Date: Wed, 08 Apr 2009 07:57:23 -0700 [thread overview]
Message-ID: <49DCBB53.2020202@redhat.com> (raw)
In-Reply-To: <20090408123133.GE18581@elte.hu>
Ingo Molnar wrote:
> * Masami Hiramatsu <mhiramat@redhat.com> wrote:
>
>> @@ -514,27 +515,39 @@ void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
>> {
>> unsigned long flags;
>> char *vaddr;
>> - struct page *pages[2];
>> + struct page *page;
>> int i;
>> + unsigned long endp = ((unsigned long)addr + len) & PAGE_MASK;
>>
>> - if (!core_kernel_text((unsigned long)addr)) {
>> - pages[0] = vmalloc_to_page(addr);
>> - pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
>> - } else {
>> - pages[0] = virt_to_page(addr);
>> - WARN_ON(!PageReserved(pages[0]));
>> - pages[1] = virt_to_page(addr + PAGE_SIZE);
>> + /*
>> + * If the written range covers 2 pages, we'll split it, because
>> + * vmalloc pages are not always continuous -- e.g. 1st page is
>> + * lowmem and 2nd page is highmem.
>> + */
>> + if (((unsigned long)addr & PAGE_MASK) != endp) {
>> + text_poke(addr, opcode, endp - (unsigned long)addr);
>> + addr = (void *)endp;
>> + opcode = (char *)opcode + (endp - (unsigned long)addr);
>> + len -= endp - (unsigned long)addr;
>> }
>> - BUG_ON(!pages[0]);
>> +
>> + if (!core_kernel_text((unsigned long)addr))
>> + page = vmalloc_to_page(addr);
>> + else
>> + page = virt_to_page(addr);
>
> hm, the bug is upstream now. And your fix turns a
> supposed-to-be-simpler kmap based patching thing back into something
> fragile looking again. We might be better off with a revert - or we
> do a real clean patch.
>
> Firstly, that core_kernel_text() distinction above looks
> artificially open-coded - dont we have a proper, generic
> "look-up-the-page" variant in the MM somewhere?
Actually, vmalloc_to_page() is generic one. It decodes
the kernel page table directly to find struct page *.
virt_to_page() is just a short-cut api.
>
>> + BUG_ON(!page);
>> local_irq_save(flags);
>> - set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
>> - if (pages[1])
>> - set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
>> - vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
>> + if (PageHighMem(page))
>> + vaddr = kmap_atomic(page, KM_TEXT_POKE);
>> + else {
>> + set_fixmap(FIX_TEXT_POKE, page_to_phys(page));
>> + vaddr = (char *)fix_to_virt(FIX_TEXT_POKE);
>> + }
>
> that too looks artificially complex. Why cannot we kmap lowmem pages
> too? If the API isnt available on !HIGHMEM kernels .. then the
> solution is to make it available, not to branch our way around it.
Hmm, why don't we enhance fixmap to handle highmem pages?
(e.g. adding set_fixmap_page())
Since kmap is only for highmem kernels, I think changing it will effects
more users...
Thank you,
>
>> memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
>> - clear_fixmap(FIX_TEXT_POKE0);
>> - if (pages[1])
>> - clear_fixmap(FIX_TEXT_POKE1);
>> + if (PageHighMem(page))
>> + kunmap_atomic(vaddr, KM_TEXT_POKE);
>> + else
>> + clear_fixmap(FIX_TEXT_POKE);
>
> ditto.
>
> Thanks,
>
> Ingo
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com
next prev parent reply other threads:[~2009-04-08 14:58 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-04 14:34 [BUG][-tip] kprobes on module functions hits kernel BUG in text_poke on x86-32 Masami Hiramatsu
2009-04-04 15:42 ` Mathieu Desnoyers
2009-04-04 18:28 ` Masami Hiramatsu
2009-04-04 19:04 ` Masami Hiramatsu
2009-04-05 3:46 ` Masami Hiramatsu
2009-04-05 3:49 ` Masami Hiramatsu
2009-04-06 17:11 ` [BUGFIX][PATCH -tip] x86: fix text_poke to handle highmem pages Masami Hiramatsu
2009-04-06 17:32 ` Mathieu Desnoyers
2009-04-06 17:44 ` Masami Hiramatsu
2009-04-06 17:58 ` Mathieu Desnoyers
2009-04-06 20:23 ` Masami Hiramatsu
2009-04-08 12:31 ` Ingo Molnar
2009-04-08 14:57 ` Masami Hiramatsu [this message]
2009-04-08 14:59 ` Ingo Molnar
2009-04-09 17:55 ` [BUGFIX][PATCH] x86: fix set_fixmap to use phys_addr_t Masami Hiramatsu
2009-04-09 18:46 ` Mathieu Desnoyers
2009-04-09 21:52 ` Masami Hiramatsu
2009-04-10 14:06 ` [tip:x86/urgent] " Masami Hiramatsu
2009-04-10 15:20 ` Masami Hiramatsu
2009-04-10 16:05 ` Mathieu Desnoyers
2009-04-10 17:48 ` Masami Hiramatsu
2009-04-10 18:30 ` Masami Hiramatsu
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