[PATCH 6/6] Add ability for SEV-ES guests to use ucalls via GHCB

Peter Gonda
2024-04-09T13:40:27Z

Modifies ucall handling for SEV-ES VMs. Instead of using an out
instruction and storing the ucall pointer in RDI, SEV-ES guests use a
outsb VMGEXIT to move the ucall pointer as the data. Allows for SEV-ES
to use ucalls instead of relying the SEV-ES MSR based termination protocol.

Cc: Vishal Annapurve <vannapurve@google.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Carlos Bilbao <carlos.bilbao@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: kvm@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Peter Gonda <pgonda@google.com>
---
.../selftests/kvm/include/x86_64/sev.h | 2 +
tools/testing/selftests/kvm/lib/x86_64/sev.c | 67 ++++++++++++++++++-
.../testing/selftests/kvm/lib/x86_64/ucall.c | 17 +++++
.../selftests/kvm/x86_64/sev_smoke_test.c | 17 +----
4 files changed, 84 insertions(+), 19 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86_64/sev.h b/tools/testing/selftests/kvm/include/x86_64/sev.h
index 691dc005e2a1..26447caccd40 100644
--- a/tools/testing/selftests/kvm/include/x86_64/sev.h
+++ b/tools/testing/selftests/kvm/include/x86_64/sev.h
@@ -109,4 +109,6 @@ static inline void sev_launch_update_data(struct kvm_vm *vm, vm_paddr_t gpa,
bool is_sev_enabled(void);
bool is_sev_es_enabled(void);

+void sev_es_ucall_port_write(uint32_t port, uint64_t data);
+
#endif /* SELFTEST_KVM_SEV_H */
diff --git a/tools/testing/selftests/kvm/lib/x86_64/sev.c b/tools/testing/selftests/kvm/lib/x86_64/sev.c
index 5b3f0a8a931a..276477f2c2cf 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/sev.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/sev.c
@@ -8,11 +8,18 @@
#include "svm.h"
#include "svm_util.h"

+#define IOIO_TYPE_STR (1 << 2)
+#define IOIO_SEG_DS (1 << 11 | 1 << 10)
+#define IOIO_DATA_8 (1 << 4)
+#define IOIO_REP (1 << 3)
+
+#define SW_EXIT_CODE_IOIO 0x7b
+
struct ghcb_entry {
struct ghcb ghcb;

/* Guest physical address of this GHCB. */
- void *gpa;
+ uint64_t gpa;

/* Host virtual address of this struct. */
struct ghcb_entry *hva;
@@ -45,16 +52,22 @@ void ghcb_init(struct kvm_vm *vm)
for (i = 0; i < KVM_MAX_VCPUS; ++i) {
entry = &hdr->ghcbs[i];
entry->hva = entry;
- entry->gpa = addr_hva2gpa(vm, &entry->ghcb);
+ entry->gpa = (uint64_t)addr_hva2gpa(vm, &entry->ghcb);
}

write_guest_global(vm, ghcb_pool, (struct ghcb_header *)vaddr);
}

+static void sev_es_terminate(void)
+{
+ wrmsr(MSR_AMD64_SEV_ES_GHCB, GHCB_MSR_TERM_REQ);
+}
+
static struct ghcb_entry *ghcb_alloc(void)
{
return &ghcb_pool->ghcbs[0];
struct ghcb_entry *entry;
+ struct ghcb *ghcb;
int i;

if (!ghcb_pool)
@@ -63,12 +76,18 @@ static struct ghcb_entry *ghcb_alloc(void)
for (i = 0; i < KVM_MAX_VCPUS; ++i) {
if (!test_and_set_bit(i, ghcb_pool->in_use)) {
entry = &ghcb_pool->ghcbs[i];
- memset(&entry->ghcb, 0, sizeof(entry->ghcb));
+ ghcb = &entry->ghcb;
+
+ memset(&ghcb, 0, sizeof(*ghcb));
+ ghcb->ghcb_usage = 0;
+ ghcb->protocol_version = 1;
+
return entry;
}
}

ucall_failed:
+ sev_es_terminate();
return NULL;
}

@@ -200,3 +219,45 @@ bool is_sev_es_enabled(void)
return is_sev_enabled() &&
rdmsr(MSR_AMD64_SEV) & MSR_AMD64_SEV_ES_ENABLED;
}
+
+static uint64_t setup_exitinfo1_portio(uint32_t port)
+{
+ uint64_t exitinfo1 = 0;
+
+ exitinfo1 |= IOIO_TYPE_STR;
+ exitinfo1 |= ((port & 0xffff) << 16);
+ exitinfo1 |= IOIO_SEG_DS;
+ exitinfo1 |= IOIO_DATA_8;
+ exitinfo1 |= IOIO_REP;
+
+ return exitinfo1;
+}
+
+static void do_vmg_exit(uint64_t ghcb_gpa)
+{
+ wrmsr(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
+ __asm__ __volatile__("rep; vmmcall");
+}
+
+void sev_es_ucall_port_write(uint32_t port, uint64_t data)
+{
+ struct ghcb_entry *entry;
+ struct ghcb *ghcb;
+ const uint64_t exitinfo1 = setup_exitinfo1_portio(port);
+
+ entry = ghcb_alloc();
+ ghcb = &entry->ghcb;
+
+ ghcb_set_sw_exit_code(ghcb, SW_EXIT_CODE_IOIO);
+ ghcb_set_sw_exit_info_1(ghcb, exitinfo1);
+ ghcb_set_sw_exit_info_2(ghcb, sizeof(data));
+
+ // Setup the SW Stratch buffer pointer.
+ ghcb_set_sw_scratch(ghcb,
+ entry->gpa + offsetof(struct ghcb, shared_buffer));
+ memcpy(&ghcb->shared_buffer, &data, sizeof(data));
+
+ do_vmg_exit(entry->gpa);
+
+ ghcb_free(entry);
+}
diff --git a/tools/testing/selftests/kvm/lib/x86_64/ucall.c b/tools/testing/selftests/kvm/lib/x86_64/ucall.c
index 1265cecc7dd1..24da2f4316d8 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/ucall.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/ucall.c
@@ -5,6 +5,8 @@
* Copyright (C) 2018, Red Hat, Inc.
*/
#include "kvm_util.h"
+#include "processor.h"
+#include "sev.h"

#define UCALL_PIO_PORT ((uint16_t)0x1000)

@@ -21,6 +23,10 @@ void ucall_arch_do_ucall(vm_vaddr_t uc)
#define HORRIFIC_L2_UCALL_CLOBBER_HACK \
"rcx", "rsi", "r8", "r9", "r10", "r11"

+ if (is_sev_es_enabled()) {
+ sev_es_ucall_port_write(UCALL_PIO_PORT, uc);
+ }
+
asm volatile("push %%rbp\n\t"
"push %%r15\n\t"
"push %%r14\n\t"
@@ -48,8 +54,19 @@ void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)

if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) {
struct kvm_regs regs;
+ uint64_t addr;
+
+ if (vcpu->vm->subtype == VM_SUBTYPE_SEV_ES) {
+ TEST_ASSERT(
+ run->io.count == 8 && run->io.size == 1,
+ "SEV-ES ucall exit requires 8 byte string out\n");
+
+ addr = *(uint64_t *)((uint8_t *)(run) + run->io.data_offset);
+ return (void *)addr;
+ }

vcpu_regs_get(vcpu, &regs);
+
return (void *)regs.rdi;
}
return NULL;
diff --git a/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c b/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c
index 1d84e78e7ae2..2448533a9a41 100644
--- a/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c
+++ b/tools/testing/selftests/kvm/x86_64/sev_smoke_test.c
@@ -18,12 +18,7 @@ static void guest_sev_es_code(void)
/* TODO: Check CPUID after GHCB-based hypercall support is added. */
GUEST_ASSERT(is_sev_es_enabled());

- /*
- * TODO: Add GHCB and ucall support for SEV-ES guests. For now, simply
- * force "termination" to signal "done" via the GHCB MSR protocol.
- */
- wrmsr(MSR_AMD64_SEV_ES_GHCB, GHCB_MSR_TERM_REQ);
- __asm__ __volatile__("rep; vmmcall");
+ GUEST_DONE();
}

static void guest_sev_code(void)
@@ -45,16 +40,6 @@ static void test_sev(void *guest_code, uint64_t policy)
for (;;) {
vcpu_run(vcpu);

- if (policy & SEV_POLICY_ES) {
- TEST_ASSERT(vcpu->run->exit_reason == KVM_EXIT_SYSTEM_EVENT,
- "Wanted SYSTEM_EVENT, got %s",
- exit_reason_str(vcpu->run->exit_reason));
- TEST_ASSERT_EQ(vcpu->run->system_event.type, KVM_SYSTEM_EVENT_SEV_TERM);
- TEST_ASSERT_EQ(vcpu->run->system_event.ndata, 1);
- TEST_ASSERT_EQ(vcpu->run->system_event.data[0], GHCB_MSR_TERM_REQ);
- break;
- }
-
switch (get_ucall(vcpu, &uc)) {
case UCALL_SYNC:
continue;
--
2.44.0.478.gd926399ef9-goog