[PATCH] KVM: SVM: Remove TSS reloading code after VMEXIT

Mingwei Zhang
2023-05-18T17:07:03Z

Remove TSS reloading code after VMEXIT since upstream KVM after [1] has
already been using VMLOAD to load host segment state (including TSS).
Therefore, reload_tss() becomes redundant. Because of that, also remove the
relevant data field tss_desc in svm_cpu_data as well as its data structure
definition.

[1] commit e79b91bb3c91 ("KVM: SVM: use vmsave/vmload for saving/restoring additionalhost state")

Reported-by: Venkatesh Srinivas <venkateshs@google.com>
Suggested-by: Jim Mattson <jmattson@google.com>
Tested-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
---
arch/x86/kvm/svm/svm.c | 24 ------------------------
arch/x86/kvm/svm/svm.h | 1 -
2 files changed, 25 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index eb308c9994f9..cfbe00360908 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -240,15 +240,6 @@ static u8 rsm_ins_bytes[] = "\x0f\xaa";

static unsigned long iopm_base;

-struct kvm_ldttss_desc {
- u16 limit0;
- u16 base0;
- unsigned base1:8, type:5, dpl:2, p:1;
- unsigned limit1:4, zero0:3, g:1, base2:8;
- u32 base3;
- u32 zero1;
-} __attribute__((packed));
-
DEFINE_PER_CPU(struct svm_cpu_data, svm_data);

/*
@@ -584,7 +575,6 @@ static int svm_hardware_enable(void)

struct svm_cpu_data *sd;
uint64_t efer;
- struct desc_struct *gdt;
int me = raw_smp_processor_id();

rdmsrl(MSR_EFER, efer);
@@ -597,9 +587,6 @@ static int svm_hardware_enable(void)
sd->next_asid = sd->max_asid + 1;
sd->min_asid = max_sev_asid + 1;

- gdt = get_current_gdt_rw();
- sd->tss_desc = (struct kvm_ldttss_desc *)(gdt + GDT_ENTRY_TSS);
-
wrmsrl(MSR_EFER, efer | EFER_SVME);

wrmsrl(MSR_VM_HSAVE_PA, sd->save_area_pa);
@@ -3453,14 +3440,6 @@ static int svm_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
return svm_invoke_exit_handler(vcpu, exit_code);
}

-static void reload_tss(struct kvm_vcpu *vcpu)
-{
- struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
-
- sd->tss_desc->type = 9; /* available 32/64-bit TSS */
- load_TR_desc();
-}
-
static void pre_svm_run(struct kvm_vcpu *vcpu)
{
struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
@@ -4064,9 +4043,6 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)

svm_vcpu_enter_exit(vcpu, spec_ctrl_intercepted);

- if (!sev_es_guest(vcpu->kvm))
- reload_tss(vcpu);
-
if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
x86_spec_ctrl_restore_host(svm->virt_spec_ctrl);

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index f44751dd8d5d..18af7e712a5a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -303,7 +303,6 @@ struct svm_cpu_data {
u32 max_asid;
u32 next_asid;
u32 min_asid;
- struct kvm_ldttss_desc *tss_desc;

struct page *save_area;
unsigned long save_area_pa;
--
2.40.1.698.g37aff9b760-goog