Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 10/16/23 08:27, 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/Kbuild                          |   2 +
>   arch/x86/include/asm/disabled-features.h |   8 +-
>   arch/x86/include/asm/msr-index.h         |  11 +-
>   arch/x86/include/asm/sev.h               |   6 +
>   arch/x86/kernel/cpu/amd.c                |  19 ++
>   arch/x86/virt/svm/Makefile               |   3 +
>   arch/x86/virt/svm/sev.c                  | 239 +++++++++++++++++++++++
>   drivers/iommu/amd/init.c                 |   2 +-
>   include/linux/amd-iommu.h                |   2 +-
>   9 files changed, 288 insertions(+), 4 deletions(-)
>   create mode 100644 arch/x86/virt/svm/Makefile
>   create mode 100644 arch/x86/virt/svm/sev.c
>
> diff --git a/arch/x86/Kbuild b/arch/x86/Kbuild
> index 5a83da703e87..6a1f36df6a18 100644
> --- a/arch/x86/Kbuild
> +++ b/arch/x86/Kbuild
> @@ -28,5 +28,7 @@ obj-y += net/
>   
>   obj-$(CONFIG_KEXEC_FILE) += purgatory/
>   
> +obj-y += virt/svm/
> +
>   # for cleaning
>   subdir- += boot tools
> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 702d93fdd10e..83efd407033b 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -117,6 +117,12 @@
>   #define DISABLE_IBT	(1 << (X86_FEATURE_IBT & 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
>    */
> @@ -141,7 +147,7 @@
>   			 DISABLE_ENQCMD)
>   #define DISABLED_MASK17	0
>   #define DISABLED_MASK18	(DISABLE_IBT)
> -#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 1d111350197f..2be74afb4cbd 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -589,6 +589,8 @@
>   #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)
> @@ -690,7 +692,14 @@
>   #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 5b4a1ce3d368..b05fcd0ab7e4 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -243,4 +243,10 @@ static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
>   static inline u64 sev_get_status(void) { return 0; }
>   #endif
>   
> +#ifdef CONFIG_KVM_AMD_SEV
> +bool snp_get_rmptable_info(u64 *start, u64 *len);
> +#else
> +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 14ee7f750cc7..6cc2074fcea3 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>
> @@ -618,6 +619,20 @@ 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;

To make this so that AutoIBRS isn't disabled should an RMP table not have 
been allocated by BIOS, lets delete the above check. It then becomes just 
a check for whether the RMP table has been allocated by BIOS, enabled by 
selecting a BIOS option, which shows intent for running SNP guests.

This way, the AutoIBRS mitigation can be used if SNP is not possible on 
the system.

Thanks,
Tom

> +
> +	return snp_get_rmptable_info(&rmp_base, &rmp_size);
> +}
> +
>   static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>   {
>   	u64 msr;
> @@ -659,6 +674,9 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>   		if (!(msr & MSR_K7_HWCR_SMMLOCK))
>   			goto clear_sev;
>   
> +		if (cpu_has(c, X86_FEATURE_SEV_SNP) && !early_rmptable_check())
> +			goto clear_snp;
> +
>   		return;
>   
>   clear_all:
> @@ -666,6 +684,7 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>   clear_sev:
>   		setup_clear_cpu_cap(X86_FEATURE_SEV);
>   		setup_clear_cpu_cap(X86_FEATURE_SEV_ES);
> +clear_snp:
>   		setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
>   	}
>   }
> 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..8b9ed72489e4
> --- /dev/null
> +++ b/arch/x86/virt/svm/sev.c
> @@ -0,0 +1,239 @@
> +// 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 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 struct rmpentry *rmptable_start __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_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_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;
> +	}
> +
> +	*start = rmp_base;
> +	*len = rmp_sz;
> +
> +	return true;
> +}
> +
> +static __init int __snp_rmptable_init(void)
> +{
> +	u64 rmp_base, rmp_size;
> +	void *rmp_start;
> +	u64 val;
> +
> +	if (!snp_get_rmptable_info(&rmp_base, &rmp_size))
> +		return 1;
> +
> +	pr_info("RMP table physical address [0x%016llx - 0x%016llx]\n",
> +		rmp_base, rmp_base + rmp_size - 1);
> +
> +	rmp_start = memremap(rmp_base, rmp_size, MEMREMAP_WB);
> +	if (!rmp_start) {
> +		pr_err("Failed to map RMP table addr 0x%llx size 0x%llx\n", rmp_base, rmp_size);
> +		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(rmp_start, 0, rmp_size);
> +
> +	/* 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:
> +	rmp_start += RMPTABLE_CPU_BOOKKEEPING_SZ;
> +	rmp_size -= RMPTABLE_CPU_BOOKKEEPING_SZ;
> +
> +	rmptable_start = (struct rmpentry *)rmp_start;
> +	rmptable_max_pfn = rmp_size / sizeof(struct rmpentry) - 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)
> +		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/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 45efb7e5d725..1c9924de607a 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3802,7 +3802,7 @@ int amd_iommu_pc_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn, u64
>   	return iommu_pc_get_set_reg(iommu, bank, cntr, fxn, value, true);
>   }
>   
> -#ifdef CONFIG_AMD_MEM_ENCRYPT
> +#ifdef CONFIG_KVM_AMD_SEV
>   int amd_iommu_snp_enable(void)
>   {
>   	/*
> diff --git a/include/linux/amd-iommu.h b/include/linux/amd-iommu.h
> index 99a5201d9e62..55fc03cb3968 100644
> --- a/include/linux/amd-iommu.h
> +++ b/include/linux/amd-iommu.h
> @@ -205,7 +205,7 @@ int amd_iommu_pc_get_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn,
>   		u64 *value);
>   struct amd_iommu *get_amd_iommu(unsigned int idx);
>   
> -#ifdef CONFIG_AMD_MEM_ENCRYPT
> +#ifdef CONFIG_KVM_AMD_SEV
>   int amd_iommu_snp_enable(void);
>   #endif
>