linux-kernel - RE: [PATCH v4 7/7] ACPI / x86: introduce acpi_os

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Date:	Tue, 15 Dec 2015 06:13:19 +0000
From:	"Chen, Yu C" <yu.c.chen@...el.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"Zheng, Lv" <lv.zheng@...el.com>
CC:	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	Andy Lutomirski <luto@...nel.org>,
	Lv Zheng <zetalog@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>
Subject: RE: [PATCH v4 7/7] ACPI / x86: introduce acpi_os_readable() support

Hi, Andy

> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@...capital.net]
> Sent: Tuesday, December 15, 2015 7:28 AM
> To: Zheng, Lv
> Cc: Wysocki, Rafael J; Brown, Len; Andy Lutomirski; Lv Zheng; linux-
> kernel@...r.kernel.org; Linux ACPI; Chen, Yu C
> Subject: Re: [PATCH v4 7/7] ACPI / x86: introduce acpi_os_readable() support
> 
> On Wed, Dec 2, 2015 at 6:43 PM, Lv Zheng <lv.zheng@...el.com> wrote:
> > From: Chen Yu <yu.c.chen@...el.com>
> >
> > This patch implements acpi_os_readable(). The function is used by
> > ACPICA AML debugger to validate user specified pointers for dumping
> > the memory as ACPICA descriptor objects.
> >
[cut]
> >
> > +bool __acpi_memory_readable(void *pointer, size_t length) {
> > +       unsigned long obj_start, obj_end;
> > +       unsigned long start_pfn, end_pfn;
> 
> What does "readable" mean in this context?
'readable' means :  the address provided by the user, 
is a dynamically allocated  virtual address -
because  the  acpi address space are allocated by 'kmalloc',
acpi debugger must check if this address is a valid 'kmalloc'
address before accessing it.

This function does the sanity check that, the vitual address is a:
1.   dynamically allocated address (beyond PAGE_OFFSET , but lower
than high_memory, VMALLOC_START, eg)
2.  besides, the physical address must be direct-mapped(so it would not be a hole).

Thanks,
yu