[RFC PATCH 38/73] KVM: x86/PVM: Handle hypercalls for privilege instruction emulation

Lai Jiangshan
2024-02-26T14:36:42Z

The privileged instructions in the PVM guest will be trapped and
emulated. To reduce the emulation overhead, some privileged instructions
in the hot path, such as RDMSR/WRMSR and TLB flushing related
instructions, will be replaced by hypercalls to improve performance.
The handling of those hypercalls is the same as the associated
privileged instruction emulation.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/pvm/pvm.c | 114 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 113 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/pvm/pvm.c b/arch/x86/kvm/pvm/pvm.c
index 2d3785e7f2f3..8d8c783c72b5 100644
--- a/arch/x86/kvm/pvm/pvm.c
+++ b/arch/x86/kvm/pvm/pvm.c
@@ -1434,6 +1434,96 @@ static int handle_synthetic_instruction_return_supervisor(struct kvm_vcpu *vcpu)
return 1;
}

+static int handle_hc_interrupt_window(struct kvm_vcpu *vcpu)
+{
+ kvm_make_request(KVM_REQ_EVENT, vcpu);
+ pvm_event_flags_update(vcpu, 0, PVM_EVENT_FLAGS_IP);
+
+ ++vcpu->stat.irq_window_exits;
+ return 1;
+}
+
+static int handle_hc_irq_halt(struct kvm_vcpu *vcpu)
+{
+ kvm_set_rflags(vcpu, kvm_get_rflags(vcpu) | X86_EFLAGS_IF);
+
+ return kvm_emulate_halt_noskip(vcpu);
+}
+
+static void pvm_flush_tlb_guest_current_kernel_user(struct kvm_vcpu *vcpu)
+{
+ /*
+ * sync the current pgd and user_pgd (pvm->msr_switch_cr3)
+ * which is a subset work of KVM_REQ_TLB_FLUSH_GUEST.
+ */
+ kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
+}
+
+/*
+ * Hypercall: PVM_HC_TLB_FLUSH
+ * Flush all TLBs.
+ */
+static int handle_hc_flush_tlb_all(struct kvm_vcpu *vcpu)
+{
+ kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
+
+ return 1;
+}
+
+/*
+ * Hypercall: PVM_HC_TLB_FLUSH_CURRENT
+ * Flush all TLBs tagged with the current CR3 and MSR_PVM_SWITCH_CR3.
+ */
+static int handle_hc_flush_tlb_current_kernel_user(struct kvm_vcpu *vcpu)
+{
+ pvm_flush_tlb_guest_current_kernel_user(vcpu);
+
+ return 1;
+}
+
+/*
+ * Hypercall: PVM_HC_TLB_INVLPG
+ * Flush TLBs associated with a single address for all tags.
+ */
+static int handle_hc_invlpg(struct kvm_vcpu *vcpu, unsigned long addr)
+{
+ kvm_mmu_invlpg(vcpu, addr);
+
+ return 1;
+}
+
+/*
+ * Hypercall: PVM_HC_RDMSR
+ * Write MSR.
+ * Return with RAX = the MSR value if succeeded.
+ * Return with RAX = 0 if it failed.
+ */
+static int handle_hc_rdmsr(struct kvm_vcpu *vcpu, u32 index)
+{
+ u64 value = 0;
+
+ kvm_get_msr(vcpu, index, &value);
+ kvm_rax_write(vcpu, value);
+
+ return 1;
+}
+
+/*
+ * Hypercall: PVM_HC_WRMSR
+ * Write MSR.
+ * Return with RAX = 0 if succeeded.
+ * Return with RAX = -EIO if it failed
+ */
+static int handle_hc_wrmsr(struct kvm_vcpu *vcpu, u32 index, u64 value)
+{
+ if (kvm_set_msr(vcpu, index, value))
+ kvm_rax_write(vcpu, -EIO);
+ else
+ kvm_rax_write(vcpu, 0);
+
+ return 1;
+}
+
static int handle_kvm_hypercall(struct kvm_vcpu *vcpu)
{
int r;
@@ -1450,6 +1540,7 @@ static int handle_exit_syscall(struct kvm_vcpu *vcpu)
{
struct vcpu_pvm *pvm = to_pvm(vcpu);
unsigned long rip = kvm_rip_read(vcpu);
+ unsigned long a0, a1;

if (!is_smod(pvm))
return do_pvm_user_event(vcpu, PVM_SYSCALL_VECTOR, false, 0);
@@ -1459,7 +1550,28 @@ static int handle_exit_syscall(struct kvm_vcpu *vcpu)
if (rip == pvm->msr_rets_rip_plus2)
return handle_synthetic_instruction_return_supervisor(vcpu);

- return handle_kvm_hypercall(vcpu);
+ a0 = kvm_rbx_read(vcpu);
+ a1 = kvm_r10_read(vcpu);
+
+ // handle hypercall, check it for pvm hypercall and then kvm hypercall
+ switch (kvm_rax_read(vcpu)) {
+ case PVM_HC_IRQ_WIN:
+ return handle_hc_interrupt_window(vcpu);
+ case PVM_HC_IRQ_HALT:
+ return handle_hc_irq_halt(vcpu);
+ case PVM_HC_TLB_FLUSH:
+ return handle_hc_flush_tlb_all(vcpu);
+ case PVM_HC_TLB_FLUSH_CURRENT:
+ return handle_hc_flush_tlb_current_kernel_user(vcpu);
+ case PVM_HC_TLB_INVLPG:
+ return handle_hc_invlpg(vcpu, a0);
+ case PVM_HC_RDMSR:
+ return handle_hc_rdmsr(vcpu, a0);
+ case PVM_HC_WRMSR:
+ return handle_hc_wrmsr(vcpu, a0, a1);
+ default:
+ return handle_kvm_hypercall(vcpu);
+ }
}

static int handle_exit_debug(struct kvm_vcpu *vcpu)
--
2.19.1.6.gb485710b