linux-kernel - Re: [PATCH v4 1/2] x86, KVM:SVM: Move sev specific parsing into arch/x86/virt/svm

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Message-ID: <776effda-641b-d504-9aab-f56d862b79dc@amd.com>
Date: Wed, 25 Sep 2024 10:57:34 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Pavan Kumar Paluri <papaluri@....com>, linux-kernel@...r.kernel.org
Cc: linux-doc@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Eric Van Tassell <Eric.VanTassell@....com>,
 Ashish Kalra <ashish.kalra@....com>, Michael Roth <michael.roth@....com>,
 "H . Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4 1/2] x86, KVM:SVM: Move sev specific parsing into
 arch/x86/virt/svm

On 9/21/24 22:36, Pavan Kumar Paluri wrote:
> Move SEV specific kernel command line option parsing support from
> arch/x86/coco/sev/core.c to arch/x86/virt/svm/cmdline.c so that both
> host and guest related SEV command line options can be supported.
> 
> No functional changes intended.
> 
> Signed-off-by: Pavan Kumar Paluri <papaluri@....com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/coco/sev/core.c          | 44 -------------------------------
>  arch/x86/include/asm/sev-common.h | 29 ++++++++++++++++++++
>  arch/x86/virt/svm/Makefile        |  1 +
>  arch/x86/virt/svm/cmdline.c       | 32 ++++++++++++++++++++++
>  4 files changed, 62 insertions(+), 44 deletions(-)
>  create mode 100644 arch/x86/virt/svm/cmdline.c
> 

...

> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 98726c2b04f8..adddcf3edaf0 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -8,6 +8,8 @@
>  #ifndef __ASM_X86_SEV_COMMON_H
>  #define __ASM_X86_SEV_COMMON_H
>  
> +#include <asm/cache.h>
> +
>  #define GHCB_MSR_INFO_POS		0
>  #define GHCB_DATA_LOW			12
>  #define GHCB_MSR_INFO_MASK		(BIT_ULL(GHCB_DATA_LOW) - 1)
> @@ -220,4 +222,31 @@ struct snp_psc_desc {
>  #define GHCB_ERR_INVALID_INPUT		5
>  #define GHCB_ERR_INVALID_EVENT		6
>  
> +struct sev_config {
> +	__u64 debug		: 1,
> +
> +	      /*
> +	       * Indicates when the per-CPU GHCB has been created and registered
> +	       * and thus can be used by the BSP instead of the early boot GHCB.
> +	       *
> +	       * For APs, the per-CPU GHCB is created before they are started
> +	       * and registered upon startup, so this flag can be used globally
> +	       * for the BSP and APs.
> +	       */
> +	      ghcbs_initialized	: 1,
> +
> +	      /*
> +	       * Indicates when the per-CPU SVSM CA is to be used instead of the
> +	       * boot SVSM CA.
> +	       *
> +	       * For APs, the per-CPU SVSM CA is created as part of the AP
> +	       * bringup, so this flag can be used globally for the BSP and APs.
> +	       */
> +	      use_cas		: 1,
> +
> +	      __reserved	: 61;
> +};
> +
> +extern struct sev_config sev_cfg __read_mostly;

So I believe the "__read_mostly" attribute really needs to be on the
actual declaration of the struct, below, in cmdline.c, right?

You can check and see which section the sev_cfg struct ends up being
placed after a build to verify.

Thanks,
Tom

> +
>  #endif
> diff --git a/arch/x86/virt/svm/Makefile b/arch/x86/virt/svm/Makefile
> index ef2a31bdcc70..eca6d71355fa 100644
> --- a/arch/x86/virt/svm/Makefile
> +++ b/arch/x86/virt/svm/Makefile
> @@ -1,3 +1,4 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  obj-$(CONFIG_KVM_AMD_SEV) += sev.o
> +obj-$(CONFIG_CPU_SUP_AMD) += cmdline.o
> diff --git a/arch/x86/virt/svm/cmdline.c b/arch/x86/virt/svm/cmdline.c
> new file mode 100644
> index 000000000000..964677ab02d6
> --- /dev/null
> +++ b/arch/x86/virt/svm/cmdline.c
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * AMD SVM-SEV command line parsing support
> + *
> + * Copyright (C) 2023 - 2024 Advanced Micro Devices, Inc.
> + *
> + * Author: Michael Roth <michael.roth@....com>
> + */
> +
> +#include <linux/string.h>
> +#include <linux/printk.h>
> +
> +#include <asm/sev-common.h>
> +
> +struct sev_config sev_cfg;
> +
> +static int __init init_sev_config(char *str)
> +{
> +	char *s;
> +
> +	while ((s = strsep(&str, ","))) {
> +		if (!strcmp(s, "debug")) {
> +			sev_cfg.debug = true;
> +			continue;
> +		}
> +
> +		pr_info("SEV command-line option '%s' was not recognized\n", s);
> +	}
> +
> +	return 1;
> +}
> +__setup("sev=", init_sev_config);