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SubjectRe: [PATCH 02/15] cxl/core: Check physical address before mapping it in devm_cxl_iomap_block()
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

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