On May 1, 2025 10:48:42 PM PDT, Xin Li <xin@xxxxxxxxx> wrote: >On 5/1/2025 11:30 AM, Sean Christopherson wrote: >> From c50fb5a8a46058bbcfdcac0a100c2aa0f7f68f1c Mon Sep 17 00:00:00 2001 >> From: Sean Christopherson<seanjc@xxxxxxxxxx> >> Date: Thu, 1 May 2025 11:10:39 -0700 >> Subject: [PATCH 2/2] x86/fred: KVM: VMX: Always use FRED for IRQ+NMI when >> CONFIG_X86_FRED=y >> >> Now that FRED provides C-code entry points for handling IRQ and NMI exits, >> use the FRED infrastructure for forwarding all such events even if FRED >> isn't supported in hardware. Avoiding the non-FRED assembly trampolines >> into the IDT handlers for IRQs eliminates the associated non-CFI indirect >> call (KVM performs a CALL by doing a lookup on the IDT using the IRQ >> vector). >> >> Force FRED for 64-bit kernels if KVM_INTEL is enabled, as the benefits of >> eliminating the IRQ trampoline usage far outwieghts the code overhead for >> FRED. >> >> Suggested-by: Peter Zijlstra<peterz@xxxxxxxxxxxxx> >> Signed-off-by: Sean Christopherson<seanjc@xxxxxxxxxx> >> --- >> arch/x86/kvm/Kconfig | 1 + >> arch/x86/kvm/vmx/vmx.c | 4 ++-- >> 2 files changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig >> index 2eeffcec5382..712a2ff28ce4 100644 >> --- a/arch/x86/kvm/Kconfig >> +++ b/arch/x86/kvm/Kconfig >> @@ -95,6 +95,7 @@ config KVM_SW_PROTECTED_VM >> config KVM_INTEL >> tristate "KVM for Intel (and compatible) processors support" >> depends on KVM && IA32_FEAT_CTL >> + select X86_FRED if X86_64 > >I LOVE this change, but not sure if everyone is happy with it. > >> select KVM_GENERIC_PRIVATE_MEM if INTEL_TDX_HOST >> select KVM_GENERIC_MEMORY_ATTRIBUTES if INTEL_TDX_HOST >> help >> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >> index ef2d7208dd20..2ea89985107d 100644 >> --- a/arch/x86/kvm/vmx/vmx.c >> +++ b/arch/x86/kvm/vmx/vmx.c >> @@ -6995,7 +6995,7 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu, >> return; >> kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ); >> - if (cpu_feature_enabled(X86_FEATURE_FRED)) >> + if (IS_ENABLED(CONFIG_X86_FRED)) > >"if (IS_ENABLED(CONFIG_X86_64))"? > >> fred_entry_from_kvm(EVENT_TYPE_EXTINT, vector); >> else >> vmx_do_interrupt_irqoff(gate_offset((gate_desc *)host_idt_base + vector)); >> @@ -7268,7 +7268,7 @@ noinstr void vmx_handle_nmi(struct kvm_vcpu *vcpu) >> return; >> kvm_before_interrupt(vcpu, KVM_HANDLING_NMI); >> - if (cpu_feature_enabled(X86_FEATURE_FRED)) >> + if (IS_ENABLED(CONFIG_X86_FRED)) > >Ditto. I don't think anyone will have a problem with compiling it in... it is such a small amount of code.
