linux-kernel - Re: [PATCH v2 2/2] tpm: tpm_crb: enhance resource mapping mechanism for supporting AMD's fTPM

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Date:   Fri, 13 Sep 2019 14:12:34 +0100
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Seunghun Han <kkamagui@...il.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        "open list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vanya Lazeev <ivan.lazeev@...il.com>
Subject: Re: [PATCH v2 2/2] tpm: tpm_crb: enhance resource mapping mechanism
 for supporting AMD's fTPM

On Wed, Sep 11, 2019 at 12:28:18AM +0900, Seunghun Han wrote:
> > Matthew pointed out that having a hook in NVS driver is better solution
> > because it is nil functionality if the TPM driver is loaded. We need
> > functions to:
> >
> > 1. Request a region from the NVS driver (when tpm_crb loads)
> > 2. Release a region back to the NVS Driver (when tpm_crb unloads).
> >
> > My proposal would unnecessarily duplicate code and also leave a
> > side-effect when TPM is not used in the first place.
> >
> > I see this as the overally best solution. If you can come up with a
> > patch for the NVS side and changes to CRB drivers to utilize the new
> > hooks, then combined with Vanya's changes we have a sustainable solution
> > for AMD fTPM.
> 
> It's a great solution. I will update this patch on your advice and
> send it to you soon.
> 
> By the way, I have a question about your advice.
> If we handle the NVS region with NVS driver, calling devm_ioremap()
> function is fine like crb_ioremap_resource() function in this patch?

No, you should reclaim the resource that conflicts and return it back
when tpm_crb is unregistered (e.g. rmmod tpm_crb).

I would try something like enumerating iomem resources with
walk_iomem_res_desc(). I would advice to peek at arch/x86/kernel/crash.c
for an example how to use this for NVS regions
(IORES_DESC_ACPI_NV_STORAGE).

E.g. you could use a callback for it along the lines of:

static int crb_find_iomem_res_cb(struct resource *res, void *io_res_ptr)
{
	struct resource *io_res = io_res_ptr;

	if (res->start == io_res->start && res->end == io_res->end) {
		/*
		 * Backup all resource data so that it can be inserted
		 * later on with the flags it had etc.
		 */
		*io_res = *res;
		return 1;
	}

	return 0;
}

Then you could __release_region() to unallocate the source. When tpm_crb
is removed you can then allocate and insert a resource with data
matching it had.


/Jarkko