[patch 37/37] x86/smpboot: Allow parallel bringup for SEV-ES

Thomas Gleixner
2023-04-14T23:47:23Z

From: David Woodhouse <dwmw@amazon.co.uk>

Enable parallel bringup for SEV-ES guests. The APs can't actually execute
the CPUID instruction directly during early startup, but they can make the
GHCB call directly instead, just as the #VC trap handler would do.

Thanks to Sabin for talking me through the way this works.

Suggested-by: Sabin Rapan <sabrapan@amazon.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

---
arch/x86/include/asm/sev-common.h | 3 +++
arch/x86/include/asm/smp.h | 1 +
arch/x86/kernel/head_64.S | 30 ++++++++++++++++++++++++++++++
arch/x86/kernel/smpboot.c | 14 ++++++++++++--
4 files changed, 46 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -70,6 +70,7 @@
/* GHCBData[63:12] */ \
(((u64)(v) & GENMASK_ULL(63, 12)) >> 12)

+#ifndef __ASSEMBLY__
/*
* SNP Page State Change Operation
*
@@ -161,6 +162,8 @@ struct snp_psc_desc {

#define GHCB_RESP_CODE(v) ((v) & GHCB_MSR_INFO_MASK)

+#endif /* __ASSEMBLY__ */
+
/*
* Error codes related to GHCB input that can be communicated back to the guest
* by setting the lower 32-bits of the GHCB SW_EXITINFO1 field to 2.
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -202,6 +202,7 @@ extern unsigned int smpboot_control;
#define STARTUP_APICID_CPUID_1F 0x80000000
#define STARTUP_APICID_CPUID_0B 0x40000000
#define STARTUP_APICID_CPUID_01 0x20000000
+#define STARTUP_APICID_SEV_ES 0x10000000

/* Top 8 bits are reserved for control */
#define STARTUP_PARALLEL_MASK 0xFF000000
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -26,6 +26,7 @@
#include <asm/nospec-branch.h>
#include <asm/fixmap.h>
#include <asm/smp.h>
+#include <asm/sev-common.h>

/*
* We are not able to switch in one step to the final KERNEL ADDRESS SPACE
@@ -243,9 +244,14 @@ SYM_INNER_LABEL(secondary_startup_64_no_
* Bit 31 STARTUP_APICID_CPUID_1F flag (use CPUID 0x1f)
* Bit 30 STARTUP_APICID_CPUID_0B flag (use CPUID 0x0b)
* Bit 29 STARTUP_APICID_CPUID_01 flag (use CPUID 0x01)
+ * Bit 28 STARTUP_APICID_SEV_ES flag (CPUID 0x0b via GHCB MSR)
* Bit 0-23 CPU# if STARTUP_APICID_CPUID_xx flags are not set
*/
movl smpboot_control(%rip), %ecx
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ testl $STARTUP_APICID_SEV_ES, %ecx
+ jnz .Luse_sev_cpuid_0b
+#endif
testl $STARTUP_APICID_CPUID_1F, %ecx
jnz .Luse_cpuid_1f
testl $STARTUP_APICID_CPUID_0B, %ecx
@@ -262,6 +268,30 @@ SYM_INNER_LABEL(secondary_startup_64_no_
shr $24, %edx
jmp .Lsetup_AP

+#ifdef CONFIG_AMD_MEM_ENCRYPT
+.Luse_sev_cpuid_0b:
+ /* Set the GHCB MSR to request CPUID 0x0B_EDX */
+ movl $MSR_AMD64_SEV_ES_GHCB, %ecx
+ movl $(GHCB_CPUID_REQ_EDX << 30) | GHCB_MSR_CPUID_REQ, %eax
+ movl $0x0b, %edx
+ wrmsr
+
+ /* Perform GHCB MSR protocol */
+ rep; vmmcall /* vmgexit */
+
+ /*
+ * Get the result. After the RDMSR:
+ * EAX should be 0xc0000005
+ * EDX should have the CPUID register value and since EDX
+ * is the target register, no need to move the result.
+ */
+ rdmsr
+ andl $GHCB_MSR_INFO_MASK, %eax
+ cmpl $GHCB_MSR_CPUID_RESP, %eax
+ jne 1f
+ jmp .Lsetup_AP
+#endif
+
.Luse_cpuid_0b:
mov $0x0B, %eax
xorl %ecx, %ecx
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -86,6 +86,7 @@
#include <asm/hw_irq.h>
#include <asm/stackprotector.h>
#include <asm/sev.h>
+#include <asm/coco.h>

/* representing HT siblings of each logical CPU */
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
@@ -1266,8 +1267,16 @@ bool __init arch_cpuhp_init_parallel_bri

/* Encrypted guests require special CPUID handling. */
if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
- pr_info("Parallel CPU startup disabled due to guest state encryption\n");
- return false;
+ switch (cc_get_vendor()) {
+ case CC_VENDOR_AMD:
+ ctrl = STARTUP_APICID_SEV_ES;
+ if (topology_extended_leaf == 0x0b)
+ goto setup;
+ fallthrough;
+ default:
+ pr_info("Parallel CPU startup disabled due to guest state encryption\n");
+ return false;
+ }
}

switch (topology_extended_leaf) {
@@ -1290,6 +1299,7 @@ bool __init arch_cpuhp_init_parallel_bri
return false;
}

+setup:
pr_debug("Parallel CPU startup enabled: 0x%08x\n", ctrl);
smpboot_control = ctrl;
return true;