[PATCH v3 0/2] nosnp sev command line support

[PATCH v3 0/2] nosnp sev command line support

[Pavan Kumar Paluri]

Provide "nosnp" boot option via "sev=nosnp" kernel command line to
prevent SEV-SNP[1] capable host kernel from enabling SEV-SNP and
initializing Reverse Map Table (RMP) [1].

On providing sev=nosnp via kernel command line:
cat /sys/module/kvm_amd/parameters/sev_snp should be "N".

This patchset is based on tip/master.

Reference:
[1] https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf

Changelog:
v2->v3:
  * Fix the build warning reported by kernel test robot
v1->v2:
  * Pick R-b's from Tom.
  * Include only those headers that provide the necessary definitions (Boris)
  * Provide appropriate references to SEV, SNP and RMP (Matthew)

---
Pavan Kumar Paluri (2):
  x86, KVM:SVM: Move sev specific parsing into arch/x86/virt/svm
  x86 KVM:SVM: Provide "nosnp" boot option for sev kernel command line

 .../arch/x86/x86_64/boot-options.rst          |  3 ++
 arch/x86/coco/sev/core.c                      | 44 -------------------
 arch/x86/include/asm/sev-common.h             | 30 +++++++++++++
 arch/x86/virt/svm/Makefile                    |  1 +
 arch/x86/virt/svm/cmdline.c                   | 39 ++++++++++++++++
 5 files changed, 73 insertions(+), 44 deletions(-)
 create mode 100644 arch/x86/virt/svm/cmdline.c


base-commit: 566644cc51d0b1ab7e98ea479808b1efd0bbe261
-- 
2.34.1

[PATCH v3 1/2] x86, KVM:SVM: Move sev specific parsing into arch/x86/virt/svm

[Pavan Kumar Paluri]

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@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/coco/sev/core.c          | 44 -------------------------------
 arch/x86/include/asm/sev-common.h | 30 +++++++++++++++++++++
 arch/x86/virt/svm/Makefile        |  1 +
 arch/x86/virt/svm/cmdline.c       | 32 ++++++++++++++++++++++
 4 files changed, 63 insertions(+), 44 deletions(-)
 create mode 100644 arch/x86/virt/svm/cmdline.c

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index de1df0cb45da..ff19e805e7a1 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -141,33 +141,6 @@ static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
 static DEFINE_PER_CPU(struct svsm_ca *, svsm_caa);
 static DEFINE_PER_CPU(u64, svsm_caa_pa);
 
-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;
-};
-
-static struct sev_config sev_cfg __read_mostly;
-
 static __always_inline bool on_vc_stack(struct pt_regs *regs)
 {
 	unsigned long sp = regs->sp;
@@ -2374,23 +2347,6 @@ static int __init report_snp_info(void)
 }
 arch_initcall(report_snp_info);
 
-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);
-
 static void update_attest_input(struct svsm_call *call, struct svsm_attest_call *input)
 {
 	/* If (new) lengths have been returned, propagate them up */
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 98726c2b04f8..d3e7f97e2a4a 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -8,6 +8,9 @@
 #ifndef __ASM_X86_SEV_COMMON_H
 #define __ASM_X86_SEV_COMMON_H
 
+#include <asm/cache.h>
+#include <asm/pgtable_types.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 +223,31 @@ 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;
+
 #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@amd.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);
-- 
2.34.1

[PATCH v3 2/2] x86 KVM:SVM: Provide "nosnp" boot option for sev kernel command line

[Pavan Kumar Paluri]

Provide a "nosnp" kernel command line option to prevent enabling of the
RMP and SEV-SNP features in the host/hypervisor. Not initializing the
RMP removes system overhead associated with RMP checks.

Co-developed-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Pavan Kumar Paluri <papaluri@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 Documentation/arch/x86/x86_64/boot-options.rst | 3 +++
 arch/x86/virt/svm/cmdline.c                    | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/Documentation/arch/x86/x86_64/boot-options.rst b/Documentation/arch/x86/x86_64/boot-options.rst
index 137432d34109..3d4e9a7dccf2 100644
--- a/Documentation/arch/x86/x86_64/boot-options.rst
+++ b/Documentation/arch/x86/x86_64/boot-options.rst
@@ -317,3 +317,6 @@ The available options are:
 
    debug
      Enable debug messages.
+
+   nosnp
+     Do not enable SEV-SNP (applies to host/hypervisor only).
diff --git a/arch/x86/virt/svm/cmdline.c b/arch/x86/virt/svm/cmdline.c
index 964677ab02d6..454574539c49 100644
--- a/arch/x86/virt/svm/cmdline.c
+++ b/arch/x86/virt/svm/cmdline.c
@@ -11,6 +11,7 @@
 #include <linux/printk.h>
 
 #include <asm/sev-common.h>
+#include <asm/cpufeature.h>
 
 struct sev_config sev_cfg;
 
@@ -24,6 +25,12 @@ static int __init init_sev_config(char *str)
 			continue;
 		}
 
+		if (!strcmp(s, "nosnp")) {
+			setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
+			cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
+			continue;
+		}
+
 		pr_info("SEV command-line option '%s' was not recognized\n", s);
 	}
 
-- 
2.34.1

Re: [PATCH v3 1/2] x86, KVM:SVM: Move sev specific parsing into arch/x86/virt/svm

[Borislav Petkov]

On Thu, Sep 05, 2024 at 09:30:55AM -0500, Pavan Kumar Paluri wrote:
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 98726c2b04f8..d3e7f97e2a4a 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -8,6 +8,9 @@
>  #ifndef __ASM_X86_SEV_COMMON_H
>  #define __ASM_X86_SEV_COMMON_H
>  
> +#include <asm/cache.h>


> +#include <asm/pgtable_types.h>

What is that include for?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v3 1/2] x86, KVM:SVM: Move sev specific parsing into arch/x86/virt/svm

[Paluri, PavanKumar]

Hello Boris,

On 9/12/2024 4:58 PM, Borislav Petkov wrote:
> On Thu, Sep 05, 2024 at 09:30:55AM -0500, Pavan Kumar Paluri wrote:
>> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
>> index 98726c2b04f8..d3e7f97e2a4a 100644
>> --- a/arch/x86/include/asm/sev-common.h
>> +++ b/arch/x86/include/asm/sev-common.h
>> @@ -8,6 +8,9 @@
>>  #ifndef __ASM_X86_SEV_COMMON_H
>>  #define __ASM_X86_SEV_COMMON_H
>>  
>> +#include <asm/cache.h>
> 
> 
>> +#include <asm/pgtable_types.h>
> 
> What is that include for?
> 

This include was a part of the diff you suggested when we had a
discussion on including only those headers that provide the definitions
for the functions we use. Here's the link to that diff:

https://lore.kernel.org/all/20240829132438.GCZtB2lqeYpleYk9c4@fat_crate.local/

I included the diff as-is and looked beyond for any more changes needed.
Should've taken a look at why the above headers were necessary.

Now that I see, <asm/pgtable_types.h> is not really needed here. While
<asm/cache.h> is needed for __read_mostly.

I will fix this for v4.

Thank you for raising this question.

- Pavan