x86/sev: Add SEV-SNP host initialization support

The memory integrity guarantees of SEV-SNP are enforced through a new
structure called the Reverse Map Table (RMP). The RMP is a single data
structure shared across the system that contains one entry for every 4K
page of DRAM that may be used by SEV-SNP VMs. The APM Volume 2 section
on Secure Nested Paging (SEV-SNP) details a number of steps needed to
detect/enable SEV-SNP and RMP table support on the host:

 - Detect SEV-SNP support based on CPUID bit
 - Initialize the RMP table memory reported by the RMP base/end MSR
   registers and configure IOMMU to be compatible with RMP access
   restrictions
 - Set the MtrrFixDramModEn bit in SYSCFG MSR
 - Set the SecureNestedPagingEn and VMPLEn bits in the SYSCFG MSR
 - Configure IOMMU

RMP table entry format is non-architectural and it can vary by
processor. It is defined by the PPR document for each respective CPU
family. Restrict SNP support to CPU models/families which are compatible
with the current RMP table entry format to guard against any undefined
behavior when running on other system types. Future models/support will
handle this through an architectural mechanism to allow for broader
compatibility.

SNP host code depends on CONFIG_KVM_AMD_SEV config flag which may be
enabled even when CONFIG_AMD_MEM_ENCRYPT isn't set, so update the
SNP-specific IOMMU helpers used here to rely on CONFIG_KVM_AMD_SEV
instead of CONFIG_AMD_MEM_ENCRYPT.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Co-developed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Co-developed-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Link: https://lore.kernel.org/r/20240126041126.1927228-5-michael.roth@amd.com

2 files changed, 219 insertions, 0 deletions

diff --git a/arch/x86/virt/svm/Makefile b/arch/x86/virt/svm/Makefile
new file mode 100644
index 000000000000..ef2a31bdcc70
--- /dev/null
+++ b/arch/x86/virt/svm/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_KVM_AMD_SEV) += sev.o
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
new file mode 100644
index 000000000000..575a9ff046cb
--- /dev/null
+++ b/arch/x86/virt/svm/sev.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AMD SVM-SEV Host Support.
+ *
+ * Copyright (C) 2023 Advanced Micro Devices, Inc.
+ *
+ * Author: Ashish Kalra <ashish.kalra@amd.com>
+ *
+ */
+
+#include <linux/cc_platform.h>
+#include <linux/printk.h>
+#include <linux/mm_types.h>
+#include <linux/set_memory.h>
+#include <linux/memblock.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/cpumask.h>
+#include <linux/iommu.h>
+#include <linux/amd-iommu.h>
+
+#include <asm/sev.h>
+#include <asm/processor.h>
+#include <asm/setup.h>
+#include <asm/svm.h>
+#include <asm/smp.h>
+#include <asm/cpu.h>
+#include <asm/apic.h>
+#include <asm/cpuid.h>
+#include <asm/cmdline.h>
+#include <asm/iommu.h>
+
+/*
+ * The RMP entry format is not architectural. The format is defined in PPR
+ * Family 19h Model 01h, Rev B1 processor.
+ */
+struct rmpentry {
+	u64	assigned	: 1,
+		pagesize	: 1,
+		immutable	: 1,
+		rsvd1		: 9,
+		gpa		: 39,
+		asid		: 10,
+		vmsa		: 1,
+		validated	: 1,
+		rsvd2		: 1;
+	u64 rsvd3;
+} __packed;
+
+/*
+ * The first 16KB from the RMP_BASE is used by the processor for the
+ * bookkeeping, the range needs to be added during the RMP entry lookup.
+ */
+#define RMPTABLE_CPU_BOOKKEEPING_SZ	0x4000
+
+static u64 probed_rmp_base, probed_rmp_size;
+static struct rmpentry *rmptable __ro_after_init;
+static u64 rmptable_max_pfn __ro_after_init;
+
+#undef pr_fmt
+#define pr_fmt(fmt)	"SEV-SNP: " fmt
+
+static int __mfd_enable(unsigned int cpu)
+{
+	u64 val;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		return 0;
+
+	rdmsrl(MSR_AMD64_SYSCFG, val);
+
+	val |= MSR_AMD64_SYSCFG_MFDM;
+
+	wrmsrl(MSR_AMD64_SYSCFG, val);
+
+	return 0;
+}
+
+static __init void mfd_enable(void *arg)
+{
+	__mfd_enable(smp_processor_id());
+}
+
+static int __snp_enable(unsigned int cpu)
+{
+	u64 val;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		return 0;
+
+	rdmsrl(MSR_AMD64_SYSCFG, val);
+
+	val |= MSR_AMD64_SYSCFG_SNP_EN;
+	val |= MSR_AMD64_SYSCFG_SNP_VMPL_EN;
+
+	wrmsrl(MSR_AMD64_SYSCFG, val);
+
+	return 0;
+}
+
+static __init void snp_enable(void *arg)
+{
+	__snp_enable(smp_processor_id());
+}
+
+#define RMP_ADDR_MASK GENMASK_ULL(51, 13)
+
+bool snp_probe_rmptable_info(void)
+{
+	u64 max_rmp_pfn, calc_rmp_sz, rmp_sz, rmp_base, rmp_end;
+
+	rdmsrl(MSR_AMD64_RMP_BASE, rmp_base);
+	rdmsrl(MSR_AMD64_RMP_END, rmp_end);
+
+	if (!(rmp_base & RMP_ADDR_MASK) || !(rmp_end & RMP_ADDR_MASK)) {
+		pr_err("Memory for the RMP table has not been reserved by BIOS\n");
+		return false;
+	}
+
+	if (rmp_base > rmp_end) {
+		pr_err("RMP configuration not valid: base=%#llx, end=%#llx\n", rmp_base, rmp_end);
+		return false;
+	}
+
+	rmp_sz = rmp_end - rmp_base + 1;
+
+	/*
+	 * Calculate the amount the memory that must be reserved by the BIOS to
+	 * address the whole RAM, including the bookkeeping area. The RMP itself
+	 * must also be covered.
+	 */
+	max_rmp_pfn = max_pfn;
+	if (PHYS_PFN(rmp_end) > max_pfn)
+		max_rmp_pfn = PHYS_PFN(rmp_end);
+
+	calc_rmp_sz = (max_rmp_pfn << 4) + RMPTABLE_CPU_BOOKKEEPING_SZ;
+
+	if (calc_rmp_sz > rmp_sz) {
+		pr_err("Memory reserved for the RMP table does not cover full system RAM (expected 0x%llx got 0x%llx)\n",
+		       calc_rmp_sz, rmp_sz);
+		return false;
+	}
+
+	probed_rmp_base = rmp_base;
+	probed_rmp_size = rmp_sz;
+
+	pr_info("RMP table physical range [0x%016llx - 0x%016llx]\n",
+		probed_rmp_base, probed_rmp_base + probed_rmp_size - 1);
+
+	return true;
+}
+
+/*
+ * Do the necessary preparations which are verified by the firmware as
+ * described in the SNP_INIT_EX firmware command description in the SNP
+ * firmware ABI spec.
+ */
+static int __init snp_rmptable_init(void)
+{
+	void *rmptable_start;
+	u64 rmptable_size;
+	u64 val;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		return 0;
+
+	if (!amd_iommu_snp_en)
+		return 0;
+
+	if (!probed_rmp_size)
+		goto nosnp;
+
+	rmptable_start = memremap(probed_rmp_base, probed_rmp_size, MEMREMAP_WB);
+	if (!rmptable_start) {
+		pr_err("Failed to map RMP table\n");
+		return 1;
+	}
+
+	/*
+	 * Check if SEV-SNP is already enabled, this can happen in case of
+	 * kexec boot.
+	 */
+	rdmsrl(MSR_AMD64_SYSCFG, val);
+	if (val & MSR_AMD64_SYSCFG_SNP_EN)
+		goto skip_enable;
+
+	memset(rmptable_start, 0, probed_rmp_size);
+
+	/* Flush the caches to ensure that data is written before SNP is enabled. */
+	wbinvd_on_all_cpus();
+
+	/* MtrrFixDramModEn must be enabled on all the CPUs prior to enabling SNP. */
+	on_each_cpu(mfd_enable, NULL, 1);
+
+	on_each_cpu(snp_enable, NULL, 1);
+
+skip_enable:
+	rmptable_start += RMPTABLE_CPU_BOOKKEEPING_SZ;
+	rmptable_size = probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ;
+
+	rmptable = (struct rmpentry *)rmptable_start;
+	rmptable_max_pfn = rmptable_size / sizeof(struct rmpentry) - 1;
+
+	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/rmptable_init:online", __snp_enable, NULL);
+
+	return 0;
+
+nosnp:
+	setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
+	return -ENOSYS;
+}
+
+/*
+ * This must be called after the IOMMU has been initialized.
+ */
+device_initcall(snp_rmptable_init);