[PATCH v6 7/8] x86/hyperv: Add smp support for SEV-SNP guest

Tianyu Lan
2023-08-16T16:00:11Z

In the AMD SEV-SNP guest, AP needs to be started up via sev es
save area and Hyper-V requires to call HVCALL_START_VP hypercall
to pass the gpa of sev es save area with AP's vp index and VTL(Virtual
trust level) parameters. Override wakeup_secondary_cpu_64 callback
with hv_snp_boot_ap.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <tiala@microsoft.com>
---
arch/x86/hyperv/ivm.c | 138 ++++++++++++++++++++++++++++++
arch/x86/include/asm/mshyperv.h | 9 ++
arch/x86/kernel/cpu/mshyperv.c | 13 ++-
include/asm-generic/hyperv-tlfs.h | 1 +
4 files changed, 159 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index b2b5cb19fac9..cbbd3af4c3da 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -18,11 +18,20 @@
#include <asm/mshyperv.h>
#include <asm/hypervisor.h>
#include <asm/mtrr.h>
+#include <asm/coco.h>
+#include <asm/io_apic.h>
+#include <asm/sev.h>
+#include <asm/realmode.h>
+#include <asm/e820/api.h>
+#include <asm/desc.h>

#ifdef CONFIG_AMD_MEM_ENCRYPT

#define GHCB_USAGE_HYPERV_CALL 1

+static u8 ap_start_input_arg[PAGE_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
+static u8 ap_start_stack[PAGE_SIZE] __aligned(PAGE_SIZE);
+
union hv_ghcb {
struct ghcb ghcb;
struct {
@@ -56,6 +65,8 @@ union hv_ghcb {
} hypercall;
} __packed __aligned(HV_HYP_PAGE_SIZE);

+static DEFINE_PER_CPU(struct sev_es_save_area *, hv_sev_vmsa);
+
static u16 hv_ghcb_version __ro_after_init;

u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size)
@@ -357,6 +368,133 @@ static bool hv_is_private_mmio(u64 addr)
return false;
}

+#define hv_populate_vmcb_seg(seg, gdtr_base) \
+do { \
+ if (seg.selector) { \
+ seg.base = 0; \
+ seg.limit = HV_AP_SEGMENT_LIMIT; \
+ seg.attrib = *(u16 *)(gdtr_base + seg.selector + 5); \
+ seg.attrib = (seg.attrib & 0xFF) | ((seg.attrib >> 4) & 0xF00); \
+ } \
+} while (0) \
+
+static int snp_set_vmsa(void *va, bool vmsa)
+{
+ u64 attrs;
+
+ /*
+ * Running at VMPL0 allows the kernel to change the VMSA bit for a page
+ * using the RMPADJUST instruction. However, for the instruction to
+ * succeed it must target the permissions of a lesser privileged
+ * (higher numbered) VMPL level, so use VMPL1 (refer to the RMPADJUST
+ * instruction in the AMD64 APM Volume 3).
+ */
+ attrs = 1;
+ if (vmsa)
+ attrs |= RMPADJUST_VMSA_PAGE_BIT;
+
+ return rmpadjust((unsigned long)va, RMP_PG_SIZE_4K, attrs);
+}
+
+static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa)
+{
+ int err;
+
+ err = snp_set_vmsa(vmsa, false);
+ if (err)
+ pr_err("clear VMSA page failed (%u), leaking page\n", err);
+ else
+ free_page((unsigned long)vmsa);
+}
+
+int hv_snp_boot_ap(int cpu, unsigned long start_ip)
+{
+ struct sev_es_save_area *vmsa = (struct sev_es_save_area *)
+ __get_free_page(GFP_KERNEL | __GFP_ZERO);
+ struct sev_es_save_area *cur_vmsa;
+ struct desc_ptr gdtr;
+ u64 ret, retry = 5;
+ struct hv_enable_vp_vtl *start_vp_input;
+ unsigned long flags;
+
+ if (!vmsa)
+ return -ENOMEM;
+
+ native_store_gdt(&gdtr);
+
+ vmsa->gdtr.base = gdtr.address;
+ vmsa->gdtr.limit = gdtr.size;
+
+ asm volatile("movl %%es, %%eax;" : "=a" (vmsa->es.selector));
+ hv_populate_vmcb_seg(vmsa->es, vmsa->gdtr.base);
+
+ asm volatile("movl %%cs, %%eax;" : "=a" (vmsa->cs.selector));
+ hv_populate_vmcb_seg(vmsa->cs, vmsa->gdtr.base);
+
+ asm volatile("movl %%ss, %%eax;" : "=a" (vmsa->ss.selector));
+ hv_populate_vmcb_seg(vmsa->ss, vmsa->gdtr.base);
+
+ asm volatile("movl %%ds, %%eax;" : "=a" (vmsa->ds.selector));
+ hv_populate_vmcb_seg(vmsa->ds, vmsa->gdtr.base);
+
+ vmsa->efer = native_read_msr(MSR_EFER);
+
+ asm volatile("movq %%cr4, %%rax;" : "=a" (vmsa->cr4));
+ asm volatile("movq %%cr3, %%rax;" : "=a" (vmsa->cr3));
+ asm volatile("movq %%cr0, %%rax;" : "=a" (vmsa->cr0));
+
+ vmsa->xcr0 = 1;
+ vmsa->g_pat = HV_AP_INIT_GPAT_DEFAULT;
+ vmsa->rip = (u64)secondary_startup_64_no_verify;
+ vmsa->rsp = (u64)&ap_start_stack[PAGE_SIZE];
+
+ /*
+ * Set the SNP-specific fields for this VMSA:
+ * VMPL level
+ * SEV_FEATURES (matches the SEV STATUS MSR right shifted 2 bits)
+ */
+ vmsa->vmpl = 0;
+ vmsa->sev_features = sev_status >> 2;
+
+ ret = snp_set_vmsa(vmsa, true);
+ if (!ret) {
+ pr_err("RMPADJUST(%llx) failed: %llx\n", (u64)vmsa, ret);
+ free_page((u64)vmsa);
+ return ret;
+ }
+
+ local_irq_save(flags);
+ start_vp_input = (struct hv_enable_vp_vtl *)ap_start_input_arg;
+ memset(start_vp_input, 0, sizeof(*start_vp_input));
+ start_vp_input->partition_id = -1;
+ start_vp_input->vp_index = cpu;
+ start_vp_input->target_vtl.target_vtl = ms_hyperv.vtl;
+ *(u64 *)&start_vp_input->vp_context = __pa(vmsa) | 1;
+
+ do {
+ ret = hv_do_hypercall(HVCALL_START_VP,
+ start_vp_input, NULL);
+ } while (hv_result(ret) == HV_STATUS_TIME_OUT && retry--);
+
+ local_irq_restore(flags);
+
+ if (!hv_result_success(ret)) {
+ pr_err("HvCallStartVirtualProcessor failed: %llx\n", ret);
+ snp_cleanup_vmsa(vmsa);
+ vmsa = NULL;
+ }
+
+ cur_vmsa = per_cpu(hv_sev_vmsa, cpu);
+ /* Free up any previous VMSA page */
+ if (cur_vmsa)
+ snp_cleanup_vmsa(cur_vmsa);
+
+ /* Record the current VMSA page */
+ per_cpu(hv_sev_vmsa, cpu) = vmsa;
+
+ return ret;
+}
+
void __init hv_vtom_init(void)
{
/*
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 8479626cd7cb..ffc419409db7 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -48,6 +48,13 @@ extern u64 hv_current_partition_id;

extern union hv_ghcb * __percpu *hv_ghcb_pg;

+/*
+ * DEFAULT INIT GPAT and SEGMENT LIMIT value in struct VMSA
+ * to start AP in enlightened SEV guest.
+ */
+#define HV_AP_INIT_GPAT_DEFAULT 0x0007040600070406ULL
+#define HV_AP_SEGMENT_LIMIT 0xffffffff
+
int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
@@ -253,12 +260,14 @@ void hv_ghcb_msr_read(u64 msr, u64 *value);
bool hv_ghcb_negotiate_protocol(void);
void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
void hv_vtom_init(void);
+int hv_snp_boot_ap(int cpu, unsigned long start_ip);
#else
static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
static inline bool hv_ghcb_negotiate_protocol(void) { return false; }
static inline void hv_ghcb_terminate(unsigned int set, unsigned int reason) {}
static inline void hv_vtom_init(void) {}
+static int hv_snp_boot_ap(int cpu, unsigned long start_ip) { return 0; }
#endif

extern bool hv_isolation_type_snp(void);
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 5398fb2f4d39..c2ccb49b49c2 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -295,6 +295,16 @@ static void __init hv_smp_prepare_cpus(unsigned int max_cpus)

native_smp_prepare_cpus(max_cpus);

+ /*
+ * Override wakeup_secondary_cpu_64 callback for SEV-SNP
+ * enlightened guest.
+ */
+ if (hv_isolation_type_en_snp())
+ apic->wakeup_secondary_cpu_64 = hv_snp_boot_ap;
+
+ if (!hv_root_partition)
+ return;
+
#ifdef CONFIG_X86_64
for_each_present_cpu(i) {
if (i == 0)
@@ -502,8 +512,7 @@ static void __init ms_hyperv_init_platform(void)

# ifdef CONFIG_SMP
smp_ops.smp_prepare_boot_cpu = hv_smp_prepare_boot_cpu;
- if (hv_root_partition)
- smp_ops.smp_prepare_cpus = hv_smp_prepare_cpus;
+ smp_ops.smp_prepare_cpus = hv_smp_prepare_cpus;
# endif

/*
diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
index f4e4cc4f965f..fdac4a1714ec 100644
--- a/include/asm-generic/hyperv-tlfs.h
+++ b/include/asm-generic/hyperv-tlfs.h
@@ -223,6 +223,7 @@ enum HV_GENERIC_SET_FORMAT {
#define HV_STATUS_INVALID_PORT_ID 17
#define HV_STATUS_INVALID_CONNECTION_ID 18
#define HV_STATUS_INSUFFICIENT_BUFFERS 19
+#define HV_STATUS_TIME_OUT 120
#define HV_STATUS_VTL_ALREADY_ENABLED 134

/*
--
2.25.1