linux-kernel - [PATCH] KVM: X86: Reduce size of kvm_vcpu_arch structure when CONFIG_KVM

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Message-ID: <CAPm50aL0Dv13EAUx3QAdVAv+Ucq2QqtVgGGnEC6t07FDn4+n5g@mail.gmail.com>
Date:   Tue, 22 Aug 2023 09:51:13 +0800
From:   Hao Peng <flyingpenghao@...il.com>
To:     pbonzini@...hat.com
Cc:     kvm@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: X86: Reduce size of kvm_vcpu_arch structure when CONFIG_KVM_XEN=n

From: Peng Hao <flyingpeng@...cent.com>

When CONFIG_KVM_XEN=n, the size of kvm_vcpu_arch can be reduced
from 5100+ to 4400+ by adding macro control.

Signed-off-by: Peng Hao <flyingpeng@...cent.com>
---
 arch/x86/include/asm/kvm_host.h | 5 ++++-
 arch/x86/kvm/cpuid.c            | 2 ++
 arch/x86/kvm/x86.c              | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3bc146dfd38d..7e85016a8a0d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -680,6 +680,7 @@ struct kvm_hypervisor_cpuid {
        u32 limit;
 };

+#ifdef CONFIG_KVM_XEN
 /* Xen HVM per vcpu emulation context */
 struct kvm_vcpu_xen {
        u64 hypercall_rip;
@@ -702,6 +703,7 @@ struct kvm_vcpu_xen {
        struct timer_list poll_timer;
        struct kvm_hypervisor_cpuid cpuid;
 };
+#endif

 struct kvm_queued_exception {
        bool pending;
@@ -912,8 +914,9 @@ struct kvm_vcpu_arch {

        bool hyperv_enabled;
        struct kvm_vcpu_hv *hyperv;
+#ifdef CONFIG_KVM_XEN
        struct kvm_vcpu_xen xen;
-
+#endif
        cpumask_var_t wbinvd_dirty_mask;

        unsigned long last_retry_eip;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7f4d13383cf2..f70a5e7db123 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -422,7 +422,9 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu,
struct kvm_cpuid_entry2 *e2,
        vcpu->arch.cpuid_nent = nent;

        vcpu->arch.kvm_cpuid = kvm_get_hypervisor_cpuid(vcpu, KVM_SIGNATURE);
+#ifdef CONFIG_KVM_XEN
        vcpu->arch.xen.cpuid = kvm_get_hypervisor_cpuid(vcpu, XEN_SIGNATURE);
+#endif
        kvm_vcpu_after_set_cpuid(vcpu);

        return 0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 278dbd37dab2..f5238b2e6cb8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3231,11 +3231,13 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)

        if (vcpu->pv_time.active)
                kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0);
+#ifdef CONFIG_KVM_XEN
        if (vcpu->xen.vcpu_info_cache.active)
                kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache,
                                        offsetof(struct
compat_vcpu_info, time));
        if (vcpu->xen.vcpu_time_info_cache.active)
                kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0);
+#endif
        kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
        return 0;
 }
--
2.31.1