From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D7B1921BAEC for ; Wed, 30 Oct 2024 15:16:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730301410; cv=none; b=nB0Vo6etoyMGcf0u3oxocPcTpu0tfROdqDybZhaP6FAGuXv4aOy//iwqxsMu7z2jszgDrVKS3Y1rDvYEIVonWqiLVdmGDoTI0grU3dQOjeTQwHOXwTBPp9+kZS9X2DM7o+0l8T6K0308oSq9Z1ApFQtfZrTaoDiTIVdCIg10Y0I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730301410; c=relaxed/simple; bh=CQTlpv6yhjHEbV/CJ9VbmZBbzh8yiW0nnuG8pOBOO9g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rZRWJZf2HcMKOoRFYpBn7UyBPPTO9lorxD2GEWzhbrwQYW6+uVUxe/4dceFTZvxRsUO/zUt2WPRnsKDET7jAzvcB5DyGkXCdZNWA0gNXKRH2G3V0FpQpPCYKhu5wuzf633UxAwcAAZLlMHJNjOSbw5WwyPoD4gSnCk/EemSPB0k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D5462113E; Wed, 30 Oct 2024 08:17:16 -0700 (PDT) Received: from [192.168.20.57] (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 247943F66E; Wed, 30 Oct 2024 08:16:44 -0700 (PDT) Message-ID: Date: Wed, 30 Oct 2024 10:16:43 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: rsi: Add automatic arm-cca-guest module loading To: Gavin Shan , linux-arm-kernel@lists.infradead.org Cc: steven.price@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, sami.mujawar@arm.com, linux-kernel@vger.kernel.org References: <20241029141114.7207-1-jeremy.linton@arm.com> <32211eb5-eed5-4c71-b62a-362d32e1af47@redhat.com> Content-Language: en-US From: Jeremy Linton In-Reply-To: <32211eb5-eed5-4c71-b62a-362d32e1af47@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi Gavin, Thanks for looking at this! On 10/29/24 7:23 PM, Gavin Shan wrote: > Hi Jeremy, > > On 10/30/24 12:11 AM, Jeremy Linton wrote: >> The TSM module provides both guest identification as well as >> attestation when a guest is run in CCA mode. Lets assure by creating a >> dummy platform device that the module is automatically loaded during >> boot. Once it is in place it can be used earlier in the boot process >> to say decrypt a LUKS rootfs. >> >> Signed-off-by: Jeremy Linton >> --- >>   arch/arm64/include/asm/rsi.h                    |  2 ++ >>   arch/arm64/kernel/rsi.c                         | 15 +++++++++++++++ >>   drivers/virt/coco/arm-cca-guest/arm-cca-guest.c |  7 +++++++ >>   3 files changed, 24 insertions(+) >> > > I don't understand how the TSM module is automatically loaded and > arm_cca_guest_init() > is triggered because of the newly introduced platform device. Could you > please provide > more details? Apart from it, some nick-picks as below. I think your asking how the module boilerplate here works, AKA how the standard uevent/udev/modalias/kmod stuff works? The short version is that the platform bus uevents an add device with a modalias and userspace udev + kmod finds matching modules, and their dependencies, and loads them which triggers the module_init() calls. The suse folks have a detailed description of how this works: https://doc.opensuse.org/documentation/leap/reference/html/book-reference/cha-udev.html#sec-udev-kernel So, this is a fairly common misuse of the platform bus, in this case to avoid needing a HWCAP. Assuring the module exists in the initrd will then result in it being loaded along any other modules required for the rootfs pivot. > >> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h >> index 188cbb9b23f5..1b14a4c4257a 100644 >> --- a/arch/arm64/include/asm/rsi.h >> +++ b/arch/arm64/include/asm/rsi.h >> @@ -10,6 +10,8 @@ >>   #include >>   #include >> +#define ARMV9_RSI_PDEV_NAME "arm-cca-dev" >> + > > Maybe 'ARMV9' can be avoided since RSI is the specific feature to ARMv9. > Besides, we already had @rsi_present there. So I would suggest to rename > it to RSI_PDEV_NAME This and the remainder of the comments below look reasonable to me, thanks! > >>   DECLARE_STATIC_KEY_FALSE(rsi_present); >>   void __init arm64_rsi_init(void); >> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c >> index 3031f25c32ef..ad963eb12921 100644 >> --- a/arch/arm64/kernel/rsi.c >> +++ b/arch/arm64/kernel/rsi.c >> @@ -8,6 +8,7 @@ >>   #include >>   #include >>   #include >> +#include >>   #include >>   #include >> @@ -140,3 +141,17 @@ void __init arm64_rsi_init(void) >>       static_branch_enable(&rsi_present); >>   } >> +static struct platform_device rsi_dev = { >> +    .name = ARMV9_RSI_PDEV_NAME, >> +    .id = -1 >> +}; >> + > >         .id = PLATFORM_DEVID_NONE, > >> +static int __init rsi_init(void) >> +{ >> +    if (is_realm_world()) >> +        if (platform_device_register(&rsi_dev)) >> +            pr_err("failed to register rsi platform device"); >> +    return 0; >> +} >> + > > Those two checks can be connected with '&&' and '\n' seems missed in the > error message. > >         if (is_realm_world() && platform_device_register(&rsi_dev)) >             pr_err("Failed to register RSI platform device\n"); > >> +arch_initcall(rsi_init) >> diff --git a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c b/ >> drivers/virt/coco/arm-cca-guest/arm-cca-guest.c >> index 488153879ec9..e7ef3b83d5d9 100644 >> --- a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c >> +++ b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c >> @@ -6,6 +6,7 @@ >>   #include >>   #include >>   #include >> +#include >>   #include >>   #include >>   #include >> @@ -219,6 +220,12 @@ static void __exit arm_cca_guest_exit(void) >>   } >>   module_exit(arm_cca_guest_exit); >> +static const struct platform_device_id arm_cca_match[] = { >> +    { ARMV9_RSI_PDEV_NAME, 0}, >> +    { } >> +}; >> + >> +MODULE_DEVICE_TABLE(platform, arm_cca_match); > > > /* Comments here to explain why @arm_cca_dev_ids[] is needed */ > static const struct platform_device_id arm_cca_dev_ids[] = { >        ... > }; > > MODULE_DEVICE_TABLE(platform, arm_cca_dev_ids); > >>   MODULE_AUTHOR("Sami Mujawar "); >>   MODULE_DESCRIPTION("Arm CCA Guest TSM Driver"); >>   MODULE_LICENSE("GPL"); > > Thanks, > Gavin >