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KVM: selftests: Reuse GPR switching logic for nVMX

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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>
Link: https://patch.msgid.link/20260728174232.2423257-6-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Yosry Ahmed 2026-07-28 17:42:24 +00:00 committed by Sean Christopherson
parent 9547309406
commit 3d31fea7b6
2 changed files with 49 additions and 66 deletions
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46
tools/testing/selftests/kvm/include/x86/evmcs.h
View File

@ -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;
}

69
tools/testing/selftests/kvm/include/x86/vmx.h
View File

@ -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;
}