[PATCH 5/6] x86/sev: Use configfs to re-enable RMP optimizations.

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@xxxxxxx>

Use configfs as an interface to re-enable RMP optimizations at runtime

When SNP guests are launched, RMPUPDATE disables the corresponding
RMPOPT optimizations. Therefore, an interface is required to manually
re-enable RMP optimizations, as no mechanism currently exists to do so
during SNP guest cleanup.

Also select CONFIG_CONFIGFS_FS when host SEV or SNP support is enabled.

Suggested-by: Thomas Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
---
 arch/x86/kvm/Kconfig    |  1 +
 arch/x86/virt/svm/sev.c | 79 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index d916bd766c94..8fb21893ec8c 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -164,6 +164,7 @@ config KVM_AMD_SEV
 	select HAVE_KVM_ARCH_GMEM_PREPARE
 	select HAVE_KVM_ARCH_GMEM_INVALIDATE
 	select HAVE_KVM_ARCH_GMEM_POPULATE
+	select CONFIGFS_FS
 	help
 	  Provides support for launching encrypted VMs which use Secure
 	  Encrypted Virtualization (SEV), Secure Encrypted Virtualization with
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 713afcc2fab3..0f71a045e4aa 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -20,6 +20,7 @@
 #include <linux/amd-iommu.h>
 #include <linux/nospec.h>
 #include <linux/kthread.h>
+#include <linux/configfs.h>
 
 #include <asm/sev.h>
 #include <asm/processor.h>
@@ -146,6 +147,10 @@ struct rmpopt_socket_config {
 	int current_node_idx;
 };
 
+#define RMPOPT_CONFIGFS_NAME	"rmpopt"
+
+static atomic_t rmpopt_in_progress = ATOMIC_INIT(0);
+
 #undef pr_fmt
 #define pr_fmt(fmt)	"SEV-SNP: " fmt
 
@@ -581,6 +586,9 @@ static int rmpopt_kthread(void *__unused)
 			cond_resched();
 		}
 
+		/* Clear in_progress flag before going to sleep */
+		atomic_set(&rmpopt_in_progress, 0);
+
 		set_current_state(TASK_INTERRUPTIBLE);
 		schedule();
 	}
@@ -595,6 +603,75 @@ static void rmpopt_all_physmem(void)
 		wake_up_process(rmpopt_task);
 }
 
+static ssize_t rmpopt_action_show(struct config_item *item, char *page)
+{
+	return sprintf(page, "RMP optimization in progress: %s\n",
+		       atomic_read(&rmpopt_in_progress) == 1 ? "Yes" : "No");
+}
+
+static ssize_t rmpopt_action_store(struct config_item *item,
+				   const char *page, size_t count)
+{
+	int in_progress_flag, ret;
+	unsigned int action;
+
+	ret = kstrtouint(page, 10, &action);
+	if (ret)
+		return ret;
+
+	if (action == 1) {
+		/* perform RMP re-optimizations */
+		in_progress_flag = atomic_cmpxchg(&rmpopt_in_progress, 0, 1);
+		if (!in_progress_flag)
+			rmpopt_all_physmem();
+	} else {
+		return -EINVAL;
+	}
+
+	return count;
+}
+
+static ssize_t rmpopt_description_show(struct config_item *item, char *page)
+{
+	return sprintf(page, "[RMPOPT]\n\necho 1 > action to perform RMP optimization.\n");
+}
+
+CONFIGFS_ATTR(rmpopt_, action);
+CONFIGFS_ATTR_RO(rmpopt_, description);
+
+static struct configfs_attribute *rmpopt_attrs[] = {
+	&rmpopt_attr_action,
+	&rmpopt_attr_description,
+	NULL,
+};
+
+static const struct config_item_type rmpopt_config_type = {
+	.ct_attrs       = rmpopt_attrs,
+	.ct_owner       = THIS_MODULE,
+};
+
+static struct configfs_subsystem rmpopt_configfs = {
+	.su_group = {
+		.cg_item = {
+		.ci_namebuf = RMPOPT_CONFIGFS_NAME,
+		.ci_type = &rmpopt_config_type,
+		},
+	},
+	.su_mutex = __MUTEX_INITIALIZER(rmpopt_configfs.su_mutex),
+};
+
+static int rmpopt_configfs_setup(void)
+{
+	int ret;
+
+	config_group_init(&rmpopt_configfs.su_group);
+	ret = configfs_register_subsystem(&rmpopt_configfs);
+	if (ret)
+		pr_err("Error %d while registering subsystem %s\n", ret, RMPOPT_CONFIGFS_NAME);
+
+	return ret;
+}
+
 static void __configure_rmpopt(void *val)
 {
 	u64 rmpopt_base = ((u64)val & PUD_MASK) | MSR_AMD64_RMPOPT_ENABLE;
@@ -770,6 +847,8 @@ static __init void configure_and_enable_rmpopt(void)
 	 */
 	rmpopt_all_physmem();
 
+	rmpopt_configfs_setup();
+
 free_cpumask:
 	free_cpumask_var(primary_threads_cpulist);
 }
-- 
2.43.0