RE: [PATCH v2 5/7] ACPI / x86: introduce acpi_os_readable() support

[Chen, Yu C]

Hi, 

> -----Original Message-----
> From: Zheng, Lv
> Sent: Wednesday, November 11, 2015 1:07 PM
> To: Chen, Yu C
> Cc: Lv Zheng; linux-kernel@xxxxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx;
> Wysocki, Rafael J; Brown, Len
> Subject: RE: [PATCH v2 5/7] ACPI / x86: introduce acpi_os_readable() support
> 
> Hi, Yu
> 
> > From: Chen, Yu C
> > Sent: Tuesday, November 10, 2015 5:43 PM
> >
> > Hi, Lv
> > Sorry for my late feedback on the patch, one minor nit below:
> >
> > > From: Zheng, Lv
> > > Sent: Tuesday, November 10, 2015 4:22 PM
> > >
> > > From: Chen Yu <yu.c.chen@xxxxxxxxx>
> > >
> > > This patch implements acpi_os_readable(). The function is used by
> > > ACPI AML debugger to validate user specified pointers for the
> > > dumpable AML operand objects.
> > >
> > > Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> > > Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx>
> > > ---
> > > +bool __acpi_memory_readable(void *pointer, size_t length) {
> > > +	unsigned long start_pfn, end_pfn;
> > > +
> > We should only check the low memory, otherwise the highmem address
> > might bring unexpected behavior in this function, I think we should add:
> > 	if (pointer  >= PAGE_OFFSET)
> > 		return false;
> 
> I think pfn_range_is_mapped() can ensure this.
virt_to_page might return an invalid page struct if pointer is not a valid kernel address.
> If you want to add some sanity checks, IMO, virt_addr_valid() could be
> better.
Yes, virt_addr_valid is better. 
> 
> > > +	start_pfn = page_to_pfn(virt_to_page(pointer));
> > > +	end_pfn = page_to_pfn(virt_to_page(pointer + length));
> > Convert pointer to char* first?
> > end_pfn = page_to_pfn(virt_to_page((char*)pointer + length));
> 
> Either a compiler supports such a conversion or a compiler ends up fatal error
> by complaining unknown sizeof(void *).
> So there is no need to do this here as the build test has passed.
> 
OK, got it, thanks.

> Thanks and best regards
> -Lv
> 
> >
> > > +	/*
> > > +	 * Since the acpi address is allocated by kmalloc, we only
> > > +	 * need to consider the direct-mapping virtual address,
> > > +	 * rather than the kmap/vmalloc/ioremap address.
> > > +	 */
> > > +	return pfn_range_is_mapped(start_pfn, end_pfn) ? true : false; }
> > > +
> > Thanks!
> >
> > Best Regards,
> > Yu
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