diff options
| author | Amit Shah <amit.shah@amd.com> | 2024-08-07 14:35:31 +0200 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-09-10 10:27:53 -0700 |
| commit | 4440337af4d415c8abf8b9b0e10c79b7518e6e3c (patch) | |
| tree | 807619e193e4acffa6fe526eb2966527b27a042f /arch/x86/kvm | |
| parent | 32071fa355e73495e509a28511a81b4baab51ff6 (diff) | |
| download | lwn-4440337af4d415c8abf8b9b0e10c79b7518e6e3c.tar.gz lwn-4440337af4d415c8abf8b9b0e10c79b7518e6e3c.zip | |
KVM: SVM: let alternatives handle the cases when RSB filling is required
Remove superfluous RSB filling after a VMEXIT when the CPU already has
flushed the RSB after a VMEXIT when AutoIBRS is enabled.
The initial implementation for adding RETPOLINES added an ALTERNATIVES
implementation for filling the RSB after a VMEXIT in commit 117cc7a908c8
("x86/retpoline: Fill return stack buffer on vmexit").
Later, X86_FEATURE_RSB_VMEXIT was added in commit 9756bba28470
("x86/speculation: Fill RSB on vmexit for IBRS") to handle stuffing the
RSB if RETPOLINE=y *or* KERNEL_IBRS=y, i.e. to also stuff the RSB if the
kernel is configured to do IBRS mitigations on entry/exit.
The AutoIBRS (on AMD) feature implementation added in commit e7862eda309e
("x86/cpu: Support AMD Automatic IBRS") used the already-implemented logic
for EIBRS in spectre_v2_determine_rsb_fill_type_on_vmexit() -- but did not
update the code at VMEXIT to act on the mode selected in that function --
resulting in VMEXITs continuing to clear the RSB when RETPOLINES are
enabled, despite the presence of AutoIBRS.
Signed-off-by: Amit Shah <amit.shah@amd.com>
Link: https://lore.kernel.org/r/20240807123531.69677-1-amit@kernel.org
[sean: massage changeloge, drop comment about AMD not needing RSB_VMEXIT_LITE]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/svm/vmenter.S | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S index a0c8eb37d3e1..2ed80aea3bb1 100644 --- a/arch/x86/kvm/svm/vmenter.S +++ b/arch/x86/kvm/svm/vmenter.S @@ -209,10 +209,8 @@ SYM_FUNC_START(__svm_vcpu_run) 7: vmload %_ASM_AX 8: -#ifdef CONFIG_MITIGATION_RETPOLINE /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */ - FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE -#endif + FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT /* Clobbers RAX, RCX, RDX. */ RESTORE_HOST_SPEC_CTRL @@ -348,10 +346,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run) 2: cli -#ifdef CONFIG_MITIGATION_RETPOLINE /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */ - FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE -#endif + FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT /* Clobbers RAX, RCX, RDX, consumes RDI (@svm) and RSI (@spec_ctrl_intercepted). */ RESTORE_HOST_SPEC_CTRL |