From mboxrd@z Thu Jan  1 00:00:00 1970
From: Huang Ying <ying.huang@intel.com>
Subject: RE: [PATCH 2/2] ACPICA: support Generic Address Structure
 bit_offset in acpi_read/write
Date: Thu, 01 Dec 2011 08:49:11 +0800
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To: "Luck, Tony" <tony.luck@intel.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Russell King <linux@arm.linux.org.uk>, Bjorn Helgaas <bhelgaas@google.com>, Thomas Renninger <trenn@suse.de>, Len Brown <lenb@kernel.org>, "Moore, Robert" <robert.moore@intel.com>, "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>, "bondd@us.ibm.com" <bondd@us.ibm.com>, Myron Stowe <myron.stowe@redhat.com>

On Thu, 2011-12-01 at 05:54 +0800, Luck, Tony wrote:
> > But as this code may be used in general acpi_read/write path too in the
> > future, can you verify whether it is harmless on ia64?
> 
> This might be a problem on ia64 - it is s/w responsibility to make sure
> that we don't map the same underlying physical address using different
> cache attributes - e.g. we must not map memory both cacheable and uncacheable
> at the same time.  Accessing such a mis-attributed page will result in a
> machine check.
> 
> So I'd worry that if the memory in question was being used as uncacheable,
> this code might result in a cached access, which would crash the machine.

+static void __iomem *acpi_map(phys_addr_t pg_off, unsigned long pg_sz)
+{
+	unsigned long pfn;
+
+	pfn = pg_off >> PAGE_SHIFT;
+	if (page_is_ram(pfn)) {
+		if (pg_sz > PAGE_SIZE)
+			return NULL;
+		return (void __iomem __force *)kmap(pfn_to_page(pfn));
+	} else
+		return ioremap(pg_off, pg_sz);
+}

Is it possible to use the page_is_ram() and kamp() path in the patch to avoid the situation you mentioned?

Best Regards,
Huang Ying