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Date:   Fri, 9 Sep 2022 14:19:11 +0200
From:   Robert Richter <rrichter@amd.com>
To:     Dan Williams <dan.j.williams@intel.com>
CC:     Alison Schofield <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Ben Widawsky <bwidawsk@kernel.org>,
        <linux-cxl@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>
Subject: Re: [PATCH 02/15] cxl/core: Check physical address before mapping it
 in devm_cxl_iomap_block()
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On 07.09.22 22:48:57, Dan Williams wrote:
> Robert Richter wrote:
> > The physical base address of a CXL range can be invalid and is then
> > set to CXL_RESOURCE_NONE. Early check this case before mapping a
> > memory block in devm_cxl_iomap_block().
> > 
> > Signed-off-by: Robert Richter <rrichter@amd.com>
> > ---
> >  drivers/cxl/core/regs.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
> > index 39a129c57d40..f216c017a474 100644
> > --- a/drivers/cxl/core/regs.c
> > +++ b/drivers/cxl/core/regs.c
> > @@ -165,6 +165,9 @@ void __iomem *devm_cxl_iomap_block(struct device *dev, resource_size_t addr,
> >  	void __iomem *ret_val;
> >  	struct resource *res;
> >  
> > +	if (addr == CXL_RESOURCE_NONE)
> > +		return NULL;
> > +
> >  	res = devm_request_mem_region(dev, addr, length, dev_name(dev));
> >  	if (!res) {
> >  		resource_size_t end = addr + length - 1;
> > -- 
> > 2.30.2
> > 
> 
> devm_request_mem_region() succeeds for you when this happens? More
> details about the failure scenario please.

No, CXL_RESOURCE_NONE (all FFs) is used as address. A broken range is
calculated that even overflows. I only vaguely remember the exact
error message.

This may happen e.g. if the Component Register Block is missing in the
DVSEC. cxl_find_regblock() may fail then and returns
CXL_RESOURCE_NONE. There are a couple of code paths there
component_reg_phys is set to CXL_RESOURCE_NONE without exiting
immediately.

I saw it during code development, when I pre-inititalized a port with
component_reg_phys set to CXL_RESOURCE_NONE. Since that case can
generally happen, I think it must be checked.

-Robert