On Thu, 18 Jan 2007, Nadia Derbey wrote: > > Trying to mmap /dev/kmem with an offset I take from /boot/System.map, > I get an EIO error on a 2.6.20-rc4. > This is something that used to work on older kernels. > > Had a look at mmap_kmem() in drivers/char/mem.c, and I'm wondering whether > pfn is correctly computed there: shouldn't we have something like > > pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) + > __pa(vma->vm_pgoff << PAGE_SHIFT); > > instead of > > pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) + vma->vm_pgoff; > > Or may be should I substract PAGE_OFFSET from the value I get from System.map > before mmapping /dev/kmem?
Sigh, you're right, 2.6.19 messed that up completely. No, you never had to subtract PAGE_OFFSET from that address in the past, and you shouldn't have to do so now. Please revert the offending patch below, and then maybe Franck can come up with a patch which preserves the original behaviour on architectures which used to work (e.g. i386), while fixing it for those architectures (which are they?) that did not. I guess it's reassuring to know that not many are actually using mmap of /dev/kmem, so you're the first to notice: thanks. Hugh From: Franck Bui-Huu <[EMAIL PROTECTED]> Date: Thu, 12 Oct 2006 19:06:33 +0000 (+0200) Subject: [PATCH] Fix up mmap_kmem X-Git-Tag: v2.6.19-rc2^0~6 X-Git-Url: http://127.0.0.1:1234/?p=.git;a=commitdiff_plain;h=99a10a60ba9bedcf5d70ef81414d3e03816afa3f;hp=a5344a9555fffd045218aced89afd6ca0f884e10 [PATCH] Fix up mmap_kmem vma->vm_pgoff is an pfn _offset_ relatif to the begining of the memory start. The previous code was doing at first: vma->vm_pgoff << PAGE_SHIFT which results into a wrong physical address since some platforms have a physical mem start that can be different from 0. After that the previous call __pa() on this wrong physical address, however __pa() is used to convert a _virtual_ address into a physical one. This patch rewrites this convertion. It calculates the pfn of PAGE_OFFSET which is the pfn of the mem start then it adds the vma->vm_pgoff to it. It also uses virt_to_phys() instead of __pa() since the latter shouldn't be used by drivers. Signed-off-by: Franck Bui-Huu <[EMAIL PROTECTED]> Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]> --- diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 6511012..a89cb52 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -292,8 +292,8 @@ static int mmap_kmem(struct file * file, { unsigned long pfn; - /* Turn a kernel-virtual address into a physical page frame */ - pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT; + /* Turn a pfn offset into an absolute pfn */ + pfn = PFN_DOWN(virt_to_phys((void *)PAGE_OFFSET)) + vma->vm_pgoff; /* * RED-PEN: on some architectures there is more mapped memory - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
