[PATCH v5 05/13] KVM: selftests: Reuse GPR switching logic for nVMX

[Yosry Ahmed <yosry@kernel.org>]

Reuse the GPR switching logic for nVMX by defining VMX_SWITCH_GPRS_ASM,
which is essentially the same as SVM_SWITCH_GPRS_ASM but also switches
RAX and doesn't switch RFLAGS, replacing the push/pop of a subset of the
registers.

The long clobber list of registers is no longer needed as registers are
saved and restored appropriately (and not clobbered by L2).

Define VMX_SWITCH_GPRS_ASM before including evmcs.h, such that it can be
used by evmcs_vmlaunch() and evmcs_vmresume().

This replaces the apparently thread-safe push/pop sequence with the
global GPR switching logic used by SVM, which isn't thread-safe at all.

However this is still an improvement because:
- The VMX logic is half-baked and prompts the UCALL clobber hack as it
  doesn't properly save/restore everything. Reusing the GPR switching
  logic used by SVM allows for dropping that hack.

- Hitting a problem due to half-baked GPR save/restore logic is arguably
  more likely than thread-safety. Evidently, adding more involved stress
  tests fails on VMX with the existing push/pop sequence. OTOH, there
  are no known failures on SVM due to lack of thread-safety fo
  save/restore. Only one test currently uses more than one vCPU with
  nested (the memstress test).

The logical next step is to move the guest_regs to be per-vCPU,
making it thread-safe for both VMX and SVM in a proper way.

Assisted-by: Gemini:gemini-3.1-pro
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
 .../testing/selftests/kvm/include/x86/evmcs.h | 46 +++++--------
 tools/testing/selftests/kvm/include/x86/vmx.h | 69 +++++++++----------
 2 files changed, 49 insertions(+), 66 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/evmcs.h b/tools/testing/selftests/kvm/include/x86/evmcs.h
index be79bda024bf1..82a8ea6b661f0 100644
--- a/tools/testing/selftests/kvm/include/x86/evmcs.h
+++ b/tools/testing/selftests/kvm/include/x86/evmcs.h
@@ -1207,30 +1207,23 @@ static inline int evmcs_vmlaunch(void)
 
 	current_evmcs->hv_clean_fields = 0;
 
-	__asm__ __volatile__("push %%rbp;"
-			     "push %%rcx;"
-			     "push %%rdx;"
-			     "push %%rsi;"
-			     "push %%rdi;"
-			     "push $0;"
+	__asm__ __volatile__("push $0;"
 			     "mov %%rsp, (%[host_rsp]);"
 			     "lea 1f(%%rip), %%rax;"
 			     "mov %%rax, (%[host_rip]);"
+			     VMX_SWITCH_GPRS_ASM
 			     "vmlaunch;"
 			     "incq (%%rsp);"
-			     "1: pop %%rax;"
-			     "pop %%rdi;"
-			     "pop %%rsi;"
-			     "pop %%rdx;"
-			     "pop %%rcx;"
-			     "pop %%rbp;"
+			     "1: ;"
+			     VMX_SWITCH_GPRS_ASM
+			     "pop %%rax;"
 			     : [ret]"=&a"(ret)
 			     : [host_rsp]"r"
 			       ((u64)&current_evmcs->host_rsp),
 			       [host_rip]"r"
-			       ((u64)&current_evmcs->host_rip)
-			     : "memory", "cc", "rbx", "r8", "r9", "r10",
-			       "r11", "r12", "r13", "r14", "r15");
+			       ((u64)&current_evmcs->host_rip),
+			       GUEST_REGS_OFFSETS
+			     : "memory", "cc");
 	return ret;
 }
 
@@ -1246,30 +1239,23 @@ static inline int evmcs_vmresume(void)
 	/* HOST_RSP */
 	current_evmcs->hv_clean_fields &= ~HV_VMX_ENLIGHTENED_CLEAN_FIELD_HOST_POINTER;
 
-	__asm__ __volatile__("push %%rbp;"
-			     "push %%rcx;"
-			     "push %%rdx;"
-			     "push %%rsi;"
-			     "push %%rdi;"
-			     "push $0;"
+	__asm__ __volatile__("push $0;"
 			     "mov %%rsp, (%[host_rsp]);"
 			     "lea 1f(%%rip), %%rax;"
 			     "mov %%rax, (%[host_rip]);"
+			     VMX_SWITCH_GPRS_ASM
 			     "vmresume;"
 			     "incq (%%rsp);"
-			     "1: pop %%rax;"
-			     "pop %%rdi;"
-			     "pop %%rsi;"
-			     "pop %%rdx;"
-			     "pop %%rcx;"
-			     "pop %%rbp;"
+			     "1: ;"
+			     VMX_SWITCH_GPRS_ASM
+			     "pop %%rax;"
 			     : [ret]"=&a"(ret)
 			     : [host_rsp]"r"
 			       ((u64)&current_evmcs->host_rsp),
 			       [host_rip]"r"
-			       ((u64)&current_evmcs->host_rip)
-			     : "memory", "cc", "rbx", "r8", "r9", "r10",
-			       "r11", "r12", "r13", "r14", "r15");
+			       ((u64)&current_evmcs->host_rip),
+			       GUEST_REGS_OFFSETS
+			     : "memory", "cc");
 	return ret;
 }
 
diff --git a/tools/testing/selftests/kvm/include/x86/vmx.h b/tools/testing/selftests/kvm/include/x86/vmx.h
index 4bcfd60e3aecb..04f5e34dea3ae 100644
--- a/tools/testing/selftests/kvm/include/x86/vmx.h
+++ b/tools/testing/selftests/kvm/include/x86/vmx.h
@@ -290,6 +290,23 @@ struct vmx_msr_entry {
 	u64 value;
 } __attribute__ ((aligned(16)));
 
+#define VMX_SWITCH_GPRS_ASM \
+	GUEST_SWITCH_GPR_ASM(rax) \
+	GUEST_SWITCH_GPR_ASM(rbx) \
+	GUEST_SWITCH_GPR_ASM(rcx) \
+	GUEST_SWITCH_GPR_ASM(rdx) \
+	GUEST_SWITCH_GPR_ASM(rbp) \
+	GUEST_SWITCH_GPR_ASM(rsi) \
+	GUEST_SWITCH_GPR_ASM(rdi) \
+	GUEST_SWITCH_GPR_ASM(r8)  \
+	GUEST_SWITCH_GPR_ASM(r9)  \
+	GUEST_SWITCH_GPR_ASM(r10) \
+	GUEST_SWITCH_GPR_ASM(r11) \
+	GUEST_SWITCH_GPR_ASM(r12) \
+	GUEST_SWITCH_GPR_ASM(r13) \
+	GUEST_SWITCH_GPR_ASM(r14) \
+	GUEST_SWITCH_GPR_ASM(r15)
+
 #include "evmcs.h"
 
 static inline int vmxon(u64 phys)
@@ -363,9 +380,6 @@ static inline u64 vmptrstz(void)
 	return value;
 }
 
-/*
- * No guest state (e.g. GPRs) is established by this vmlaunch.
- */
 static inline int vmlaunch(void)
 {
 	int ret;
@@ -373,34 +387,24 @@ static inline int vmlaunch(void)
 	if (enable_evmcs)
 		return evmcs_vmlaunch();
 
-	__asm__ __volatile__("push %%rbp;"
-			     "push %%rcx;"
-			     "push %%rdx;"
-			     "push %%rsi;"
-			     "push %%rdi;"
-			     "push $0;"
+	__asm__ __volatile__("push $0;"
 			     "vmwrite %%rsp, %[host_rsp];"
 			     "lea 1f(%%rip), %%rax;"
 			     "vmwrite %%rax, %[host_rip];"
+			     VMX_SWITCH_GPRS_ASM
 			     "vmlaunch;"
 			     "incq (%%rsp);"
-			     "1: pop %%rax;"
-			     "pop %%rdi;"
-			     "pop %%rsi;"
-			     "pop %%rdx;"
-			     "pop %%rcx;"
-			     "pop %%rbp;"
+			     "1: ;"
+			     VMX_SWITCH_GPRS_ASM
+			     "pop %%rax;"
 			     : [ret]"=&a"(ret)
 			     : [host_rsp]"r"((u64)HOST_RSP),
-			       [host_rip]"r"((u64)HOST_RIP)
-			     : "memory", "cc", "rbx", "r8", "r9", "r10",
-			       "r11", "r12", "r13", "r14", "r15");
+			       [host_rip]"r"((u64)HOST_RIP),
+			       GUEST_REGS_OFFSETS
+			     : "memory", "cc");
 	return ret;
 }
 
-/*
- * No guest state (e.g. GPRs) is established by this vmresume.
- */
 static inline int vmresume(void)
 {
 	int ret;
@@ -408,28 +412,21 @@ static inline int vmresume(void)
 	if (enable_evmcs)
 		return evmcs_vmresume();
 
-	__asm__ __volatile__("push %%rbp;"
-			     "push %%rcx;"
-			     "push %%rdx;"
-			     "push %%rsi;"
-			     "push %%rdi;"
-			     "push $0;"
+	__asm__ __volatile__("push $0;"
 			     "vmwrite %%rsp, %[host_rsp];"
 			     "lea 1f(%%rip), %%rax;"
 			     "vmwrite %%rax, %[host_rip];"
+			     VMX_SWITCH_GPRS_ASM
 			     "vmresume;"
 			     "incq (%%rsp);"
-			     "1: pop %%rax;"
-			     "pop %%rdi;"
-			     "pop %%rsi;"
-			     "pop %%rdx;"
-			     "pop %%rcx;"
-			     "pop %%rbp;"
+			     "1: ;"
+			     VMX_SWITCH_GPRS_ASM
+			     "pop %%rax;"
 			     : [ret]"=&a"(ret)
 			     : [host_rsp]"r"((u64)HOST_RSP),
-			       [host_rip]"r"((u64)HOST_RIP)
-			     : "memory", "cc", "rbx", "r8", "r9", "r10",
-			       "r11", "r12", "r13", "r14", "r15");
+			       [host_rip]"r"((u64)HOST_RIP),
+			       GUEST_REGS_OFFSETS
+			     : "memory", "cc");
 	return ret;
 }
 
-- 
2.55.0.487.gaf234c4eb3-goog