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Date: Fri, 26 Jan 2024 16:45:46 -0800
From: Dionna Amalie Glaze <dionnaglaze@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Dan Williams <dan.j.williams@...el.com>, Michael Roth <michael.roth@....com>,
Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH 04/11] x86/sev: Use kernel provided SVSM Calling Areas
On Fri, Jan 26, 2024 at 2:17 PM Tom Lendacky <thomas.lendacky@....com> wrote:
>
> The SVSM Calling Area (CA) is used to communicate between Linux and the
> SVSM. Since the firmware supplied CA for the BSP is likely to be in
> reserved memory, switch off that CA to a kernel provided CA so that access
> and use of the CA is available during boot. The CA switch is done using
> the SVSM core protocol SVSM_CORE_REMAP_CAA call.
REMAP_CA, not CAA.
>
> An SVSM call is executed by filling out the SVSM CA and setting the proper
> register state as documented by the SVSM protocol. The SVSM is invoked by
> by requesting the hypervisor to run VMPL0.
>
> Once it is safe to allocate/reserve memory, allocate a CA for each CPU.
> After allocating the new CAs, the BSP will switch from the boot CA to the
> per-CPU CA. The CA for an AP is identified to the SVSM when creating the
> VMSA in preparation for booting the AP.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
> arch/x86/include/asm/sev-common.h | 13 ++
> arch/x86/include/asm/sev.h | 32 +++++
> arch/x86/include/uapi/asm/svm.h | 1 +
> arch/x86/kernel/sev-shared.c | 94 +++++++++++++-
> arch/x86/kernel/sev.c | 207 +++++++++++++++++++++++++-----
> arch/x86/mm/mem_encrypt_amd.c | 8 +-
> 6 files changed, 320 insertions(+), 35 deletions(-)
>
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 68a8cdf6fd6a..71db5ba020b9 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -96,6 +96,19 @@ enum psc_op {
> /* GHCBData[63:32] */ \
> (((u64)(val) & GENMASK_ULL(63, 32)) >> 32)
>
> +/* GHCB Run at VMPL Request/Response */
> +#define GHCB_MSR_VMPL_REQ 0x016
> +#define GHCB_MSR_VMPL_REQ_LEVEL(v) \
> + /* GHCBData[39:32] */ \
> + (((u64)(v) & GENMASK_ULL(7, 0) << 32) | \
> + /* GHCBDdata[11:0] */ \
> + GHCB_MSR_VMPL_REQ)
> +
> +#define GHCB_MSR_VMPL_RESP 0x017
> +#define GHCB_MSR_VMPL_RESP_VAL(v) \
> + /* GHCBData[63:32] */ \
> + (((u64)(v) & GENMASK_ULL(63, 32)) >> 32)
> +
> /* GHCB Hypervisor Feature Request/Response */
> #define GHCB_MSR_HV_FT_REQ 0x080
> #define GHCB_MSR_HV_FT_RESP 0x081
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 207c315041ba..2f1e583769fc 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -163,6 +163,36 @@ struct svsm_ca {
> u8 svsm_buffer[PAGE_SIZE - 8];
> };
>
> +#define SVSM_SUCCESS 0
> +#define SVSM_ERR_INCOMPLETE 0x80000000
> +#define SVSM_ERR_UNSUPPORTED_PROTOCOL 0x80000001
> +#define SVSM_ERR_UNSUPPORTED_CALL 0x80000002
> +#define SVSM_ERR_INVALID_ADDRESS 0x80000003
> +#define SVSM_ERR_INVALID_FORMAT 0x80000004
> +#define SVSM_ERR_INVALID_PARAMETER 0x80000005
> +#define SVSM_ERR_INVALID_REQUEST 0x80000006
> +#define SVSM_ERR_BUSY 0x80000007
> +
> +/*
> + * SVSM protocol structure
> + */
> +struct svsm_call {
> + struct svsm_ca *caa;
> + u64 rax;
> + u64 rcx;
> + u64 rdx;
> + u64 r8;
> + u64 r9;
> + u64 rax_out;
> + u64 rcx_out;
> + u64 rdx_out;
> + u64 r8_out;
> + u64 r9_out;
> +};
> +
> +#define SVSM_CORE_CALL(x) ((0ULL << 32) | (x))
Given that we should expect to see other SVSM protocols used in the
kernel, should we not have
#define SVSM_PROTOCOL_CALL(protocol, call) (((unsigned long)(protocol)
<< 32) | (call))
#define SVSM_CORE_PROTOCOL 0
#define SVSM_ATTESTATION_PROTOCOL 1
#define SVSM_VTPM_PROTOCOL 2
And then
#define SVSM_CORE_CALL(x) SVSM_PROTOCOL_CALL(SVSM_CORE_PROTOCOL, x)
or be cute and use symbol concatenation like
#define SVSM_PROTOCOL_ID(id) SVSM_##id##_PROTOCOL
#define SVSM_CALL(id, call) SVSM_PROTOCOL_CALL(SVSM_PROTOCOL_ID(id), call)
So you can just do SVSM_CALL(CORE, 0) ?
> +#define SVSM_CORE_REMAP_CA 0
> +
> #ifdef CONFIG_AMD_MEM_ENCRYPT
> extern void __sev_es_ist_enter(struct pt_regs *regs);
> extern void __sev_es_ist_exit(void);
> @@ -236,6 +266,7 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct sn
> void snp_accept_memory(phys_addr_t start, phys_addr_t end);
> u64 snp_get_unsupported_features(u64 status);
> u64 sev_get_status(void);
> +void __init snp_remap_svsm_ca(void);
> #else
> static inline void sev_es_ist_enter(struct pt_regs *regs) { }
> static inline void sev_es_ist_exit(void) { }
> @@ -264,6 +295,7 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
> static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
> static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
> static inline u64 sev_get_status(void) { return 0; }
> +static inline void snp_remap_svsm_ca(void) { }
> #endif
>
> #endif
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index 80e1df482337..1814b413fd57 100644
> --- a/arch/x86/include/uapi/asm/svm.h
> +++ b/arch/x86/include/uapi/asm/svm.h
> @@ -115,6 +115,7 @@
> #define SVM_VMGEXIT_AP_CREATE_ON_INIT 0
> #define SVM_VMGEXIT_AP_CREATE 1
> #define SVM_VMGEXIT_AP_DESTROY 2
> +#define SVM_VMGEXIT_SNP_RUN_VMPL 0x80000018
> #define SVM_VMGEXIT_HV_FEATURES 0x8000fffd
> #define SVM_VMGEXIT_TERM_REQUEST 0x8000fffe
> #define SVM_VMGEXIT_TERM_REASON(reason_set, reason_code) \
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index 99170f129eef..7e9fa5d8889b 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -14,7 +14,9 @@
> #define has_cpuflag(f) boot_cpu_has(f)
> #else
> #undef WARN
> -#define WARN(condition, format...) (!!(condition))
> +#define WARN(condition, format...) (!!(condition))
> +#undef vc_forward_exception
> +#define vc_forward_exception(c) panic("SNP: Hypervisor requested exception\n")
> #endif
>
> /* I/O parameters for CPUID-related helpers */
> @@ -240,6 +242,96 @@ static enum es_result verify_exception_info(struct ghcb *ghcb, struct es_em_ctxt
> return ES_VMM_ERROR;
> }
>
> +static __always_inline void issue_svsm_call(struct svsm_call *call, u8 *pending)
> +{
> + /*
> + * Issue the VMGEXIT to run the SVSM:
> + * - Load the SVSM register state (RAX, RCX, RDX, R8 and R9)
> + * - Set the CA call pending field to 1
> + * - Issue VMGEXIT
> + * - Save the SVSM return register state (RAX, RCX, RDX, R8 and R9)
> + * - Perform atomic exchange of the CA call pending field
> + */
> + asm volatile("mov %9, %%r8\n\t"
> + "mov %10, %%r9\n\t"
> + "movb $1, %11\n\t"
> + "rep; vmmcall\n\t"
> + "mov %%r8, %3\n\t"
> + "mov %%r9, %4\n\t"
> + "xchgb %5, %11\n\t"
> + : "=a" (call->rax_out), "=c" (call->rcx_out), "=d" (call->rdx_out),
> + "=m" (call->r8_out), "=m" (call->r9_out),
> + "+r" (*pending)
> + : "a" (call->rax), "c" (call->rcx), "d" (call->rdx),
> + "r" (call->r8), "r" (call->r9),
> + "m" (call->caa->call_pending)
> + : "r8", "r9", "memory");
> +}
> +
> +static int __svsm_msr_protocol(struct svsm_call *call)
> +{
> + u64 val, resp;
> + u8 pending;
> +
> + val = sev_es_rd_ghcb_msr();
> +
> + sev_es_wr_ghcb_msr(GHCB_MSR_VMPL_REQ_LEVEL(0));
> +
> + pending = 0;
> + issue_svsm_call(call, &pending);
> +
> + resp = sev_es_rd_ghcb_msr();
> +
> + sev_es_wr_ghcb_msr(val);
> +
> + if (pending)
> + return -EINVAL;
> +
> + if (GHCB_RESP_CODE(resp) != GHCB_MSR_VMPL_RESP)
> + return -EINVAL;
> +
> + if (GHCB_MSR_VMPL_RESP_VAL(resp) != 0)
> + return -EINVAL;
> +
> + return call->rax_out;
> +}
> +
> +static int __svsm_ghcb_protocol(struct ghcb *ghcb, struct svsm_call *call)
> +{
> + struct es_em_ctxt ctxt;
> + u8 pending;
> +
> + vc_ghcb_invalidate(ghcb);
> +
> + /* Fill in protocol and format specifiers */
> + ghcb->protocol_version = ghcb_version;
> + ghcb->ghcb_usage = GHCB_DEFAULT_USAGE;
> +
> + ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_SNP_RUN_VMPL);
> + ghcb_set_sw_exit_info_1(ghcb, 0);
> + ghcb_set_sw_exit_info_2(ghcb, 0);
> +
> + sev_es_wr_ghcb_msr(__pa(ghcb));
> +
> + pending = 0;
> + issue_svsm_call(call, &pending);
> +
> + if (pending)
> + return -EINVAL;
> +
> + switch (verify_exception_info(ghcb, &ctxt)) {
> + case ES_OK:
> + break;
> + case ES_EXCEPTION:
> + vc_forward_exception(&ctxt);
> + fallthrough;
> + default:
> + return -EINVAL;
> + }
> +
> + return call->rax_out;
> +}
> +
> static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
> struct es_em_ctxt *ctxt,
> u64 exit_code, u64 exit_info_1,
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 7066afaa8133..3bd7860fbfe1 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -114,6 +114,8 @@ struct ghcb_state {
>
> static DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);
> static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
> +static DEFINE_PER_CPU(struct svsm_ca *, svsm_caa);
> +static DEFINE_PER_CPU(u64, svsm_caa_pa);
>
> /*
> * SVSM related information:
> @@ -121,6 +123,7 @@ static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
> * non-zero. The VMPL is therefore used to indicate the presence of an SVSM.
> */
> static u8 vmpl __ro_after_init;
> +static struct svsm_ca boot_svsm_ca_page __aligned(PAGE_SIZE);
> static struct svsm_ca *boot_svsm_caa __ro_after_init;
> static u64 boot_svsm_caa_pa __ro_after_init;
>
> @@ -138,11 +141,26 @@ struct sev_config {
> */
> ghcbs_initialized : 1,
>
> + /*
> + * A flag used to indicate when the per-CPU SVSM CA is to be
> + * used instead of the boot SVSM CA.
> + *
> + * For APs, the per-CPU SVSM CA is created as part of the AP
> + * bringup, so this flag can be used globally for the BSP and APs.
> + */
> + cas_initialized : 1,
> +
> __reserved : 62;
> };
>
> static struct sev_config sev_cfg __read_mostly;
>
> +static struct svsm_ca *__svsm_get_caa(void)
> +{
> + return sev_cfg.cas_initialized ? this_cpu_read(svsm_caa)
> + : boot_svsm_caa;
> +}
> +
> static __always_inline bool on_vc_stack(struct pt_regs *regs)
> {
> unsigned long sp = regs->sp;
> @@ -560,6 +578,33 @@ static enum es_result vc_ioio_check(struct es_em_ctxt *ctxt, u16 port, size_t si
> return ES_EXCEPTION;
> }
>
> +static __always_inline void vc_forward_exception(struct es_em_ctxt *ctxt)
> +{
> + long error_code = ctxt->fi.error_code;
> + int trapnr = ctxt->fi.vector;
> +
> + ctxt->regs->orig_ax = ctxt->fi.error_code;
> +
> + switch (trapnr) {
> + case X86_TRAP_GP:
> + exc_general_protection(ctxt->regs, error_code);
> + break;
> + case X86_TRAP_UD:
> + exc_invalid_op(ctxt->regs);
> + break;
> + case X86_TRAP_PF:
> + write_cr2(ctxt->fi.cr2);
> + exc_page_fault(ctxt->regs, error_code);
> + break;
> + case X86_TRAP_AC:
> + exc_alignment_check(ctxt->regs, error_code);
> + break;
> + default:
> + pr_emerg("Unsupported exception in #VC instruction emulation - can't continue\n");
> + BUG();
> + }
> +}
> +
> /* Include code shared with pre-decompression boot stage */
> #include "sev-shared.c"
>
> @@ -588,6 +633,42 @@ static noinstr void __sev_put_ghcb(struct ghcb_state *state)
> }
> }
>
> +static int svsm_protocol(struct svsm_call *call)
> +{
> + struct ghcb_state state;
> + unsigned long flags;
> + struct ghcb *ghcb;
> + int ret;
> +
> + /*
> + * This can be called very early in the boot, use native functions in
> + * order to avoid paravirt issues.
> + */
> + flags = native_save_fl();
> + if (flags & X86_EFLAGS_IF)
> + native_irq_disable();
> +
> + if (sev_cfg.ghcbs_initialized)
> + ghcb = __sev_get_ghcb(&state);
> + else if (boot_ghcb)
> + ghcb = boot_ghcb;
> + else
> + ghcb = NULL;
> +
> + do {
> + ret = ghcb ? __svsm_ghcb_protocol(ghcb, call)
> + : __svsm_msr_protocol(call);
> + } while (ret == SVSM_ERR_BUSY);
> +
> + if (sev_cfg.ghcbs_initialized)
> + __sev_put_ghcb(&state);
> +
> + if (flags & X86_EFLAGS_IF)
> + native_irq_enable();
> +
> + return ret;
> +}
> +
> void noinstr __sev_es_nmi_complete(void)
> {
> struct ghcb_state state;
> @@ -1348,6 +1429,18 @@ static void __init alloc_runtime_data(int cpu)
> panic("Can't allocate SEV-ES runtime data");
>
> per_cpu(runtime_data, cpu) = data;
> +
> + if (vmpl) {
> + struct svsm_ca *caa;
> +
> + /* Allocate the SVSM CA page if an SVSM is present */
> + caa = memblock_alloc(sizeof(*caa), PAGE_SIZE);
> + if (!caa)
> + panic("Can't allocate SVSM CA page\n");
> +
> + per_cpu(svsm_caa, cpu) = caa;
> + per_cpu(svsm_caa_pa, cpu) = __pa(caa);
> + }
> }
>
> static void __init init_ghcb(int cpu)
> @@ -1397,6 +1490,31 @@ void __init sev_es_init_vc_handling(void)
> init_ghcb(cpu);
> }
>
> + /* If running under an SVSM, switch to the per-cpu CA */
> + if (vmpl) {
> + struct svsm_call call = {};
> + unsigned long flags;
> + int ret;
> +
> + local_irq_save(flags);
> +
> + /*
> + * SVSM_CORE_REMAP_CA call:
> + * RAX = 0 (Protocol=0, CallID=0)
> + * RCX = New CA GPA
> + */
> + call.caa = __svsm_get_caa();
> + call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
> + call.rcx = this_cpu_read(svsm_caa_pa);
> + ret = svsm_protocol(&call);
> + if (ret != SVSM_SUCCESS)
> + panic("Can't remap the SVSM CA, ret=%#x (%d)\n", ret, ret);
> +
> + sev_cfg.cas_initialized = true;
> +
> + local_irq_restore(flags);
> + }
> +
> sev_es_setup_play_dead();
>
> /* Secondary CPUs use the runtime #VC handler */
> @@ -1818,33 +1936,6 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
> return result;
> }
>
> -static __always_inline void vc_forward_exception(struct es_em_ctxt *ctxt)
> -{
> - long error_code = ctxt->fi.error_code;
> - int trapnr = ctxt->fi.vector;
> -
> - ctxt->regs->orig_ax = ctxt->fi.error_code;
> -
> - switch (trapnr) {
> - case X86_TRAP_GP:
> - exc_general_protection(ctxt->regs, error_code);
> - break;
> - case X86_TRAP_UD:
> - exc_invalid_op(ctxt->regs);
> - break;
> - case X86_TRAP_PF:
> - write_cr2(ctxt->fi.cr2);
> - exc_page_fault(ctxt->regs, error_code);
> - break;
> - case X86_TRAP_AC:
> - exc_alignment_check(ctxt->regs, error_code);
> - break;
> - default:
> - pr_emerg("Unsupported exception in #VC instruction emulation - can't continue\n");
> - BUG();
> - }
> -}
> -
> static __always_inline bool is_vc2_stack(unsigned long sp)
> {
> return (sp >= __this_cpu_ist_bottom_va(VC2) && sp < __this_cpu_ist_top_va(VC2));
> @@ -2094,6 +2185,52 @@ static __init struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
> return cc_info;
> }
>
> +static __init void setup_svsm(struct cc_blob_sev_info *cc_info)
> +{
> + struct svsm_call call = {};
> + int ret;
> + u64 pa;
> +
> + /*
> + * Record the SVSM Calling Area address (CAA) if the guest is not
> + * running at VMPL0. The CA will be used to communicate with the
> + * SVSM to perform the SVSM services.
> + */
> + setup_svsm_ca(cc_info);
> +
> + /* Nothing to do if not running under an SVSM. */
> + if (!vmpl)
> + return;
> +
> + /*
> + * It is very early in the boot and the kernel is running identity
> + * mapped but without having adjusted the pagetables to where the
> + * kernel was loaded (physbase), so the get the CA address using
the get the -> get the
> + * RIP-relative addressing.
> + */
> + asm volatile ("lea boot_svsm_ca_page(%%rip), %0"
> + : "=r" (pa)
> + : "p" (&boot_svsm_ca_page));
> +
> + /*
> + * Switch over to the boot SVSM CA while the current CA is still
> + * addressable. There is no GHCB at this point so use the MSR protocol.
> + *
> + * SVSM_CORE_REMAP_CA call:
> + * RAX = 0 (Protocol=0, CallID=0)
> + * RCX = New CA GPA
> + */
> + call.caa = __svsm_get_caa();
> + call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
> + call.rcx = pa;
> + ret = svsm_protocol(&call);
> + if (ret != SVSM_SUCCESS)
> + panic("Can't remap the SVSM CA, ret=%#x (%d)\n", ret, ret);
> +
> + boot_svsm_caa = (struct svsm_ca *)pa;
> + boot_svsm_caa_pa = pa;
> +}
> +
> bool __init snp_init(struct boot_params *bp)
> {
> struct cc_blob_sev_info *cc_info;
> @@ -2107,12 +2244,7 @@ bool __init snp_init(struct boot_params *bp)
>
> setup_cpuid_table(cc_info);
>
> - /*
> - * Record the SVSM Calling Area address (CAA) if the guest is not
> - * running at VMPL0. The CA will be used to communicate with the
> - * SVSM to perform the SVSM services.
> - */
> - setup_svsm_ca(cc_info);
> + setup_svsm(cc_info);
>
> /*
> * The CC blob will be used later to access the secrets page. Cache
> @@ -2278,3 +2410,12 @@ static int __init snp_init_platform_device(void)
> return 0;
> }
> device_initcall(snp_init_platform_device);
> +
> +void __init snp_remap_svsm_ca(void)
> +{
> + if (!vmpl)
> + return;
> +
> + /* Update the CAA to a proper kernel address */
> + boot_svsm_caa = &boot_svsm_ca_page;
> +}
> diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
> index 70b91de2e053..8943286f9fdc 100644
> --- a/arch/x86/mm/mem_encrypt_amd.c
> +++ b/arch/x86/mm/mem_encrypt_amd.c
> @@ -2,7 +2,7 @@
> /*
> * AMD Memory Encryption Support
> *
> - * Copyright (C) 2016 Advanced Micro Devices, Inc.
> + * Copyright (C) 2016-2024 Advanced Micro Devices, Inc.
> *
> * Author: Tom Lendacky <thomas.lendacky@....com>
> */
> @@ -492,6 +492,12 @@ void __init sme_early_init(void)
> */
> if (sev_status & MSR_AMD64_SEV_ENABLED)
> ia32_disable();
> +
> + /*
> + * Switch the SVSM CA mapping (if active) from identity mapped to
> + * kernel mapped.
> + */
> + snp_remap_svsm_ca();
> }
>
> void __init mem_encrypt_free_decrypted_mem(void)
> --
> 2.42.0
>
>
--
-Dionna Glaze, PhD (she/her)
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