From: Seunghun Han <email@example.com> To: Jarkko Sakkinen <firstname.lastname@example.org> Cc: Peter Huewe <email@example.com>, Matthew Garrett <firstname.lastname@example.org>, "open list:TPM DEVICE DRIVER" <email@example.com>, Linux Kernel Mailing List <firstname.lastname@example.org>, Vanya Lazeev <email@example.com> Subject: Re: [PATCH v2 2/2] tpm: tpm_crb: enhance resource mapping mechanism for supporting AMD's fTPM Date: Mon, 16 Sep 2019 17:18:33 +0900 [thread overview] Message-ID: <CAHjaAcQ07nDbb1NAg4m7bK8szSKVi7b55m7epzxPJjxxttaT0A@mail.gmail.com> (raw) In-Reply-To: <20190913131234.GA7412@linux.intel.com> > > > 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 > > 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. Thank you for your sincere advice, and I have some questions about it. As you know, the core reason of this ACPI NVS problem is that a busy bit is set to the ACPI NVS area. So, devm_ioremap_resource() function fails because of it. If we want to call devm_ioremap_resource() for this case, we maybe need to rearrange the existing memory layout from the child relationship to the sibling relationship below. We also need to get back when tpm_crb unloads. [ ACPI NVS (parent) [ TPM CMD buffer (child of NVS) ] [ TPM RSP buffer (child of NVS) ] ] <---> [ ACPI NVS head ] [ CMD buffer ] [ NVS middle ] [ RSP buffer ] [ NVS tails ] Our concern is a race condition between NVS driver and TPM CRB driver. In my view, we could solve this problem if we only make and call the functions you said, requesting and releasing a region from NVS driver. NVS driver doesn't rely on iomem layout, and it relies on internal nvs_list data. Therefore, I added some details to your guide. How about this sequence? 1) When tpm_crb driver loads, the driver checks if command/response buffers are in ACPI NVS area. If so, it requests (or removes) the buffer regions from NVS driver's nvs_list (with suspend_nvs_unregister() function I will add to the nvs.c driver). 2) If command/response buffers are in ACPI NVS area, tpm_crb driver calls devm_ioremap() instead of devm_ioremap_resource() like this patch. 3) When tpm_crb driver unloads, the driver releases (or adds) the buffer regions to NVS driver's nvs_list (with existing suspend_nvs_register() function in the nvs.c driver). I think the sequence could solve the problem we concerned. What do you think about the sequence? Seunghun
next prev parent reply other threads:[~2019-09-16 8:18 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-09-09 9:09 [PATCH v2 0/2] Enhance support for the " Seunghun Han 2019-09-09 9:09 ` [PATCH v2 1/2] tpm: tpm_crb: enhance command and response buffer size calculation code Seunghun Han 2019-09-10 12:34 ` Jarkko Sakkinen 2019-09-10 15:12 ` Seunghun Han 2019-09-09 9:09 ` [PATCH v2 2/2] tpm: tpm_crb: enhance resource mapping mechanism for supporting AMD's fTPM Seunghun Han 2019-09-10 14:42 ` Jarkko Sakkinen 2019-09-10 15:06 ` Jarkko Sakkinen 2019-09-10 15:28 ` Seunghun Han 2019-09-13 13:12 ` Jarkko Sakkinen 2019-09-16 8:18 ` Seunghun Han [this message] 2019-09-16 8:42 ` Seunghun Han
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