Re: [PATCH RFC v9 07/51] x86/sev: Add the host SEV-SNP initialization support

From: Jeremi Piotrowski
Date: Wed Aug 09 2023 - 09:03:52 EST

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On Sun, Jun 11, 2023 at 11:25:15PM -0500, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@xxxxxxx>
>
> 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. APM2 section 15.36 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. 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.
>
> Co-developed-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Co-developed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> [mdr: rework commit message to be clearer about what patch does, squash
> in early_rmptable_check() handling from Tom]
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
> arch/x86/coco/Makefile | 1 +
> arch/x86/coco/sev/Makefile | 3 +
> arch/x86/coco/sev/host.c | 212 +++++++++++++++++++++++
> arch/x86/include/asm/disabled-features.h | 8 +-
> arch/x86/include/asm/msr-index.h | 11 +-
> arch/x86/include/asm/sev.h | 2 +
> arch/x86/kernel/cpu/amd.c | 19 ++
> drivers/iommu/amd/init.c | 2 +-
> include/linux/amd-iommu.h | 2 +-
> 9 files changed, 256 insertions(+), 4 deletions(-)
> create mode 100644 arch/x86/coco/sev/Makefile
> create mode 100644 arch/x86/coco/sev/host.c
>
> diff --git a/arch/x86/coco/Makefile b/arch/x86/coco/Makefile
> index 6aa52e719bf5..6a7d876130e2 100644
> --- a/arch/x86/coco/Makefile
> +++ b/arch/x86/coco/Makefile
> @@ -6,3 +6,4 @@ CFLAGS_core.o += -fno-stack-protector
> obj-$(CONFIG_ARCH_HAS_CC_PLATFORM) += core.o
>
> obj-$(CONFIG_INTEL_TDX_GUEST) += tdx/
> +obj-$(CONFIG_KVM_AMD_SEV) += sev/
> diff --git a/arch/x86/coco/sev/Makefile b/arch/x86/coco/sev/Makefile
> new file mode 100644
> index 000000000000..27c0500d75c8
> --- /dev/null
> +++ b/arch/x86/coco/sev/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-y += host.o
> diff --git a/arch/x86/coco/sev/host.c b/arch/x86/coco/sev/host.c
> new file mode 100644
> index 000000000000..6907ce887b23
> --- /dev/null
> +++ b/arch/x86/coco/sev/host.c
> @@ -0,0 +1,212 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * AMD SVM-SEV Host Support.
> + *
> + * Copyright (C) 2023 Advanced Micro Devices, Inc.
> + *
> + * Author: Ashish Kalra <ashish.kalra@xxxxxxx>
> + *
> + */
> +
> +#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 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 unsigned long rmptable_start __ro_after_init;
> +static unsigned long rmptable_end __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());
> +}
> +
> +bool snp_get_rmptable_info(u64 *start, u64 *len)
> +{
> + 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_end) {
> + pr_err("Memory for the RMP table has not been reserved by BIOS\n");
> + 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;
> + }
> +
> + *start = rmp_base;
> + *len = rmp_sz;
> +
> + return true;
> +}
> +
> +static __init int __snp_rmptable_init(void)
> +{
> + u64 rmp_base, sz;
> + void *start;
> + u64 val;
> +
> + if (!snp_get_rmptable_info(&rmp_base, &sz))
> + return 1;
> +
> + pr_info("RMP table physical address [0x%016llx - 0x%016llx]\n",
> + rmp_base, rmp_base + sz - 1);
> +
> + start = memremap(rmp_base, sz, MEMREMAP_WB);
> + if (!start) {
> + pr_err("Failed to map RMP table addr 0x%llx size 0x%llx\n", rmp_base, sz);
> + 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;
> +
> + /* Initialize the RMP table to zero */
> + memset(start, 0, sz);
> +
> + /* Flush the caches to ensure that data is written before SNP is enabled. */
> + wbinvd_on_all_cpus();
> +
> + /* MFDM must be enabled on all the CPUs prior to enabling SNP. */
> + on_each_cpu(mfd_enable, NULL, 1);
> +
> + /* Enable SNP on all CPUs. */
> + on_each_cpu(snp_enable, NULL, 1);
> +
> +skip_enable:
> + rmptable_start = (unsigned long)start;
> + rmptable_end = rmptable_start + sz - 1;
> +
> + return 0;
> +}
> +
> +static int __init snp_rmptable_init(void)
> +{
> + int family, model;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> + return 0;
> +
> + family = boot_cpu_data.x86;
> + model = boot_cpu_data.x86_model;
> +
> + /*
> + * RMP table entry format is not architectural and it can vary by processor and
> + * is defined by the per-processor PPR. Restrict SNP support on the known CPU
> + * model and family for which the RMP table entry format is currently defined for.
> + */
> + if (!(family == 0x19 && model <= 0xaf) && !(family == 0x1a && model <= 0xf))
> + goto nosnp;
> +
> + if (amd_iommu_snp_enable())
> + goto nosnp;
> +
> + if (__snp_rmptable_init())
> + goto nosnp;
> +
> + 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 PCI subsystem. This is because amd_iommu_snp_enable()
> + * is called to ensure the IOMMU supports the SEV-SNP feature, which can only be
> + * called after subsys_initcall().
> + *
> + * NOTE: IOMMU is enforced by SNP to ensure that hypervisor cannot program DMA
> + * directly into guest private memory. In case of SNP, the IOMMU ensures that
> + * the page(s) used for DMA are hypervisor owned.
> + */
> +fs_initcall(snp_rmptable_init);
> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 5dfa4fb76f4b..0a9938aea305 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -99,6 +99,12 @@
> # define DISABLE_TDX_GUEST (1 << (X86_FEATURE_TDX_GUEST & 31))
> #endif
>
> +#ifdef CONFIG_KVM_AMD_SEV
> +# define DISABLE_SEV_SNP 0
> +#else
> +# define DISABLE_SEV_SNP (1 << (X86_FEATURE_SEV_SNP & 31))
> +#endif
> +
> /*
> * Make sure to add features to the correct mask
> */
> @@ -123,7 +129,7 @@
> DISABLE_ENQCMD)
> #define DISABLED_MASK17 0
> #define DISABLED_MASK18 0
> -#define DISABLED_MASK19 0
> +#define DISABLED_MASK19 (DISABLE_SEV_SNP)
> #define DISABLED_MASK20 0
> #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 21)
>
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index ad35355ee43e..db0f3a041930 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -574,6 +574,8 @@
> #define MSR_AMD64_SEV_ENABLED BIT_ULL(MSR_AMD64_SEV_ENABLED_BIT)
> #define MSR_AMD64_SEV_ES_ENABLED BIT_ULL(MSR_AMD64_SEV_ES_ENABLED_BIT)
> #define MSR_AMD64_SEV_SNP_ENABLED BIT_ULL(MSR_AMD64_SEV_SNP_ENABLED_BIT)
> +#define MSR_AMD64_RMP_BASE 0xc0010132
> +#define MSR_AMD64_RMP_END 0xc0010133
>
> /* SNP feature bits enabled by the hypervisor */
> #define MSR_AMD64_SNP_VTOM BIT_ULL(3)
> @@ -675,7 +677,14 @@
> #define MSR_K8_TOP_MEM2 0xc001001d
> #define MSR_AMD64_SYSCFG 0xc0010010
> #define MSR_AMD64_SYSCFG_MEM_ENCRYPT_BIT 23
> -#define MSR_AMD64_SYSCFG_MEM_ENCRYPT BIT_ULL(MSR_AMD64_SYSCFG_MEM_ENCRYPT_BIT)
> +#define MSR_AMD64_SYSCFG_MEM_ENCRYPT BIT_ULL(MSR_AMD64_SYSCFG_MEM_ENCRYPT_BIT)
> +#define MSR_AMD64_SYSCFG_SNP_EN_BIT 24
> +#define MSR_AMD64_SYSCFG_SNP_EN BIT_ULL(MSR_AMD64_SYSCFG_SNP_EN_BIT)
> +#define MSR_AMD64_SYSCFG_SNP_VMPL_EN_BIT 25
> +#define MSR_AMD64_SYSCFG_SNP_VMPL_EN BIT_ULL(MSR_AMD64_SYSCFG_SNP_VMPL_EN_BIT)
> +#define MSR_AMD64_SYSCFG_MFDM_BIT 19
> +#define MSR_AMD64_SYSCFG_MFDM BIT_ULL(MSR_AMD64_SYSCFG_MFDM_BIT)
> +
> #define MSR_K8_INT_PENDING_MSG 0xc0010055
> /* C1E active bits in int pending message */
> #define K8_INTP_C1E_ACTIVE_MASK 0x18000000
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ebc271bb6d8e..d34c46db7dd1 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -197,6 +197,7 @@ void snp_set_wakeup_secondary_cpu(void);
> bool snp_init(struct boot_params *bp);
> void __init __noreturn snp_abort(void);
> int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err);
> +bool snp_get_rmptable_info(u64 *start, u64 *len);
> #else
> static inline void sev_es_ist_enter(struct pt_regs *regs) { }
> static inline void sev_es_ist_exit(void) { }
> @@ -221,6 +222,7 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
> {
> return -ENOTTY;
> }
> +static inline bool snp_get_rmptable_info(u64 *start, u64 *len) { return false; }
> #endif
>
> #endif
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index a79774181f22..1493ddf89fdf 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -20,6 +20,7 @@
> #include <asm/delay.h>
> #include <asm/debugreg.h>
> #include <asm/resctrl.h>
> +#include <asm/sev.h>
>
> #ifdef CONFIG_X86_64
> # include <asm/mmconfig.h>
> @@ -546,6 +547,20 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
> resctrl_cpu_detect(c);
> }
>
> +static bool early_rmptable_check(void)
> +{
> + u64 rmp_base, rmp_size;
> +
> + /*
> + * For early BSP initialization, max_pfn won't be set up yet, wait until
> + * it is set before performing the RMP table calculations.
> + */
> + if (!max_pfn)
> + return true;
> +
> + return snp_get_rmptable_info(&rmp_base, &rmp_size);
> +}
> +

When CONFIG_AMD_MEM_ENCRYPT=y && CONFIG_KVM=n (=> CONFIG_KVM_AMD_SEV=n) this
results in an undefined reference to snp_get_rmptable_info when linking this
file. The header provides a stub when AMD_MEM_ENCRYPT=n but the definition is
only compiled in when KVM_AMD_SEV=y

Jeremi

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