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Subject[PATCH v10 14/16] KVM: x86: Add guest support for detecting and enabling SEV Live Migration feature.
Date
From: Ashish Kalra <ashish.kalra@amd.com>

The guest support for detecting and enabling SEV Live migration
feature uses the following logic :

- kvm_init_plaform() invokes check_kvm_sev_migration() which
checks if its booted under the EFI

- If not EFI,

i) check for the KVM_FEATURE_CPUID

ii) if CPUID reports that migration is supported, issue a wrmsrl()
to enable the SEV live migration support

- If EFI,

i) check for the KVM_FEATURE_CPUID

ii) If CPUID reports that migration is supported, read the UEFI variable which
indicates OVMF support for live migration

iii) the variable indicates live migration is supported, issue a wrmsrl() to
enable the SEV live migration support

The EFI live migration check is done using a late_initcall() callback.

Also, ensure that _bss_decrypted section is marked as decrypted in the
shared pages list.

Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
arch/x86/include/asm/mem_encrypt.h | 8 +++++
arch/x86/kernel/kvm.c | 52 ++++++++++++++++++++++++++++++
arch/x86/mm/mem_encrypt.c | 41 +++++++++++++++++++++++
3 files changed, 101 insertions(+)

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 31c4df123aa0..19b77f3a62dc 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -21,6 +21,7 @@
extern u64 sme_me_mask;
extern u64 sev_status;
extern bool sev_enabled;
+extern bool sev_live_migration_enabled;

void sme_encrypt_execute(unsigned long encrypted_kernel_vaddr,
unsigned long decrypted_kernel_vaddr,
@@ -44,8 +45,11 @@ void __init sme_enable(struct boot_params *bp);

int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
+void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages,
+ bool enc);

void __init mem_encrypt_free_decrypted_mem(void);
+void __init check_kvm_sev_migration(void);

/* Architecture __weak replacement functions */
void __init mem_encrypt_init(void);
@@ -60,6 +64,7 @@ bool sev_es_active(void);
#else /* !CONFIG_AMD_MEM_ENCRYPT */

#define sme_me_mask 0ULL
+#define sev_live_migration_enabled false

static inline void __init sme_early_encrypt(resource_size_t paddr,
unsigned long size) { }
@@ -84,8 +89,11 @@ static inline int __init
early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0; }
static inline int __init
early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }
+static inline void __init
+early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages, bool enc) {}

static inline void mem_encrypt_free_decrypted_mem(void) { }
+static inline void check_kvm_sev_migration(void) { }

#define __bss_decrypted

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01ca3b4..c4b8029c1442 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -26,6 +26,7 @@
#include <linux/kprobes.h>
#include <linux/nmi.h>
#include <linux/swait.h>
+#include <linux/efi.h>
#include <asm/timer.h>
#include <asm/cpu.h>
#include <asm/traps.h>
@@ -429,6 +430,56 @@ static inline void __set_percpu_decrypted(void *ptr, unsigned long size)
early_set_memory_decrypted((unsigned long) ptr, size);
}

+static int __init setup_kvm_sev_migration(void)
+{
+ efi_char16_t efi_sev_live_migration_enabled[] = L"SevLiveMigrationEnabled";
+ efi_guid_t efi_variable_guid = MEM_ENCRYPT_GUID;
+ efi_status_t status;
+ unsigned long size;
+ bool enabled;
+
+ /*
+ * check_kvm_sev_migration() invoked via kvm_init_platform() before
+ * this callback would have setup the indicator that live migration
+ * feature is supported/enabled.
+ */
+ if (!sev_live_migration_enabled)
+ return 0;
+
+ if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+ pr_info("%s : EFI runtime services are not enabled\n", __func__);
+ return 0;
+ }
+
+ size = sizeof(enabled);
+
+ /* Get variable contents into buffer */
+ status = efi.get_variable(efi_sev_live_migration_enabled,
+ &efi_variable_guid, NULL, &size, &enabled);
+
+ if (status == EFI_NOT_FOUND) {
+ pr_info("%s : EFI live migration variable not found\n", __func__);
+ return 0;
+ }
+
+ if (status != EFI_SUCCESS) {
+ pr_info("%s : EFI variable retrieval failed\n", __func__);
+ return 0;
+ }
+
+ if (enabled == 0) {
+ pr_info("%s: live migration disabled in EFI\n", __func__);
+ return 0;
+ }
+
+ pr_info("%s : live migration enabled in EFI\n", __func__);
+ wrmsrl(MSR_KVM_SEV_LIVE_MIGRATION, KVM_SEV_LIVE_MIGRATION_ENABLED);
+
+ return true;
+}
+
+late_initcall(setup_kvm_sev_migration);
+
/*
* Iterate through all possible CPUs and map the memory region pointed
* by apf_reason, steal_time and kvm_apic_eoi as decrypted at once.
@@ -747,6 +798,7 @@ static bool __init kvm_msi_ext_dest_id(void)

static void __init kvm_init_platform(void)
{
+ check_kvm_sev_migration();
kvmclock_init();
x86_platform.apic_post_init = kvm_apic_init;
}
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index dc17d14f9bcd..f80d2aee3938 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -20,6 +20,7 @@
#include <linux/bitops.h>
#include <linux/dma-mapping.h>
#include <linux/kvm_para.h>
+#include <linux/efi.h>

#include <asm/tlbflush.h>
#include <asm/fixmap.h>
@@ -48,6 +49,8 @@ EXPORT_SYMBOL_GPL(sev_enable_key);

bool sev_enabled __section(".data");

+bool sev_live_migration_enabled __section(".data");
+
/* Buffer used for early in-place encryption by BSP, no locking needed */
static char sme_early_buffer[PAGE_SIZE] __initdata __aligned(PAGE_SIZE);

@@ -237,6 +240,9 @@ static void set_memory_enc_dec_hypercall(unsigned long vaddr, int npages,
unsigned long sz = npages << PAGE_SHIFT;
unsigned long vaddr_end, vaddr_next;

+ if (!sev_live_migration_enabled)
+ return;
+
vaddr_end = vaddr + sz;

for (; vaddr < vaddr_end; vaddr = vaddr_next) {
@@ -407,6 +413,12 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size)
return early_set_memory_enc_dec(vaddr, size, true);
}

+void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages,
+ bool enc)
+{
+ set_memory_enc_dec_hypercall(vaddr, npages, enc);
+}
+
/*
* SME and SEV are very similar but they are not the same, so there are
* times that the kernel will need to distinguish between SME and SEV. The
@@ -461,6 +473,35 @@ bool force_dma_unencrypted(struct device *dev)
return false;
}

+void __init check_kvm_sev_migration(void)
+{
+ if (sev_active() &&
+ kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION)) {
+ unsigned long nr_pages;
+
+ pr_info("KVM enable live migration\n");
+ sev_live_migration_enabled = true;
+
+ /*
+ * Ensure that _bss_decrypted section is marked as decrypted in the
+ * shared pages list.
+ */
+ nr_pages = DIV_ROUND_UP(__end_bss_decrypted - __start_bss_decrypted,
+ PAGE_SIZE);
+ early_set_mem_enc_dec_hypercall((unsigned long)__start_bss_decrypted,
+ nr_pages, 0);
+
+ /*
+ * If not booted using EFI, enable Live migration support.
+ */
+ if (!efi_enabled(EFI_BOOT))
+ wrmsrl(MSR_KVM_SEV_LIVE_MIGRATION,
+ KVM_SEV_LIVE_MIGRATION_ENABLED);
+ } else {
+ pr_info("KVM enable live migration feature unsupported\n");
+ }
+}
+
void __init mem_encrypt_free_decrypted_mem(void)
{
unsigned long vaddr, vaddr_end, npages;
--
2.17.1
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