On Wed, Dec 14, 2022 at 01:40:06PM -0600, 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. The goal of RMP is to
> track the owner of each page of memory. Pages of memory can be owned by
> the hypervisor, owned by a specific VM or owned by the AMD-SP. See APM2
> section 15.36.3 for more detail on RMP.
>
> The RMP table is used to enforce access control to memory. The table itself
> is not directly writable by the software. New CPU instructions (RMPUPDATE,
> PVALIDATE, RMPADJUST) are used to manipulate the RMP entries.
>
> Based on the platform configuration, the BIOS reserves the memory used
> for the RMP table. The start and end address of the RMP table must be
> queried by reading the RMP_BASE and RMP_END MSRs. If the RMP_BASE and
> RMP_END are not set then disable the SEV-SNP feature.
>
> The SEV-SNP feature is enabled only after the RMP table is successfully
> initialized.
>
> Also set SYSCFG.MFMD when enabling SNP as SEV-SNP FW >= 1.51 requires
> that SYSCFG.MFMD must be se
>
> RMP table entry format is non-architectural and it can vary by processor
> and is defined by the PPR. Restrict SNP support on the known CPU model
> and family for which the RMP table entry format is currently defined for.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-b: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
> arch/x86/include/asm/disabled-features.h | 8 +-
> arch/x86/include/asm/msr-index.h | 11 +-
> arch/x86/kernel/sev.c | 180 +++++++++++++++++++++++
> 3 files changed, 197 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 33d2cd04d254..9b5a2cc8064a 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -87,6 +87,12 @@
> # define DISABLE_TDX_GUEST (1 << (X86_FEATURE_TDX_GUEST & 31))
> #endif
>
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +# 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
> */
> @@ -110,7 +116,7 @@
> DISABLE_ENQCMD)
> #define DISABLED_MASK17 0
> #define DISABLED_MASK18 0
> -#define DISABLED_MASK19 0
> +#define DISABLED_MASK19 (DISABLE_SEV_SNP)
> #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 20)
>
> #endif /* _ASM_X86_DISABLED_FEATURES_H */
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 10ac52705892..35100c630617 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -565,6 +565,8 @@
> #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
>
> #define MSR_AMD64_VIRT_SPEC_CTRL 0xc001011f
>
> @@ -649,7 +651,14 @@
> #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/kernel/sev.c b/arch/x86/kernel/sev.c
> index a428c62330d3..687a91284506 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -22,6 +22,9 @@
> #include <linux/efi.h>
> #include <linux/platform_device.h>
> #include <linux/io.h>
> +#include <linux/cpumask.h>
> +#include <linux/iommu.h>
> +#include <linux/amd-iommu.h>
>
> #include <asm/cpu_entry_area.h>
> #include <asm/stacktrace.h>
> @@ -38,6 +41,7 @@
> #include <asm/apic.h>
> #include <asm/cpuid.h>
> #include <asm/cmdline.h>
> +#include <asm/iommu.h>
>
> #define DR7_RESET_VALUE 0x400
>
> @@ -57,6 +61,12 @@
> #define AP_INIT_CR0_DEFAULT 0x60000010
> #define AP_INIT_MXCSR_DEFAULT 0x1f80
>
> +/*
> + * 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
> +
> /* For early boot hypervisor communication in SEV-ES enabled guests */
> static struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
>
> @@ -69,6 +79,9 @@ static struct ghcb *boot_ghcb __section(".data");
> /* Bitmap of SEV features supported by the hypervisor */
> static u64 sev_hv_features __ro_after_init;
>
> +static unsigned long rmptable_start __ro_after_init;
> +static unsigned long rmptable_end __ro_after_init;
> +
> /* #VC handler runtime per-CPU data */
> struct sev_es_runtime_data {
> struct ghcb ghcb_page;
> @@ -2260,3 +2273,170 @@ static int __init snp_init_platform_device(void)
> return 0;
> }
> device_initcall(snp_init_platform_device);
> +
> +#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());
> +}
> +
> +static bool get_rmptable_info(u64 *start, u64 *len)
> +{
> + u64 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. The reserved memory should also cover the
> + * RMP table itself.
> + */
> + calc_rmp_sz = (((rmp_sz >> PAGE_SHIFT) + totalram_pages()) << 4) + RMPTABLE_CPU_BOOKKEEPING_SZ;
Since the rmptable is indexed by page number, I believe this check should be
using max_pfn:
calc_rmp_sz = (max_pfn << 4) + RMPTABLE_CPU_BOOKKEEPING_SZ;
This accounts for holes/offsets in the memory map which lead to the top of
memory having pfn > totalram_pages().
> +
> + 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;
> +
> + pr_info("RMP table physical address [0x%016llx - 0x%016llx]\n", rmp_base, rmp_end);
> +
> + return true;
> +}
> +
> +static __init int __snp_rmptable_init(void)
> +{
> + u64 rmp_base, sz;
> + void *start;
> + u64 val;
> +
> + if (!get_rmptable_info(&rmp_base, &sz))
> + return 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)
> + 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);
> --
> 2.25.1
>
