linux-kernel - [RFC] LoongArch: KVM: Handle interrupt early before enabling irq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-Id: <20250220084306.323967-1-maobibo@loongson.cn>
Date: Thu, 20 Feb 2025 16:43:06 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: [RFC] LoongArch: KVM: Handle interrupt early before enabling irq

If interrupt arrive when vCPU is running, vCPU will exit because of
interrupt exception. Currently interrupt exception is handled after
local_irq_enable() is called, and it is handled by host kernel rather
than KVM hypervisor. It will introduce extra another interrupt
exception and then host will handle irq.

If KVM hypervisor detect that it is interrupt exception, interrupt
can be handle early in KVM hypervisor before local_irq_enable() is
called.

On 3C5000 dual-way machine, there will be 10% -- 15% performance
improvement with netperf UDP_RR option with 10G ethernet card.
                   original     with patch    improvement
  netperf UDP_RR     7200          8100           +12%

The total performance is low because irqchip is emulated in qemu VMM,
however from the same testbed, there is performance improvement
actually.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/kernel/traps.c |  1 +
 arch/loongarch/kvm/vcpu.c     | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index 2ec3106c0da3..eed0d8b02ee3 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -1114,6 +1114,7 @@ asmlinkage void noinstr do_vint(struct pt_regs *regs, unsigned long sp)
 
 	irqentry_exit(regs, state);
 }
+EXPORT_SYMBOL(do_vint);
 
 unsigned long eentry;
 unsigned long tlbrentry;
diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
index 20f941af3e9e..775f7aa6d904 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -5,6 +5,7 @@
 
 #include <linux/kvm_host.h>
 #include <linux/entry-kvm.h>
+#include <asm/exception.h>
 #include <asm/fpu.h>
 #include <asm/lbt.h>
 #include <asm/loongarch.h>
@@ -304,6 +305,17 @@ static int kvm_pre_enter_guest(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
+static void kvm_handle_irq(struct kvm_vcpu *vcpu)
+{
+	struct pt_regs regs;
+
+	/* Construct pseudo pt_regs, only necessary registers is added */
+	regs.csr_prmd = CSR_PRMD_PIE;
+	regs.csr_era = vcpu->arch.pc;
+	regs.regs[3] = vcpu->arch.host_sp;
+	do_vint(&regs, (unsigned long)&regs);
+}
+
 /*
  * Return 1 for resume guest and "<= 0" for resume host.
  */
@@ -323,6 +335,12 @@ static int kvm_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
 
 	guest_timing_exit_irqoff();
 	guest_state_exit_irqoff();
+	/*
+	 * VM exit because of host interrupt
+	 * Handle irq directly before enabling irq
+	 */
+	if (!ecode && intr)
+		kvm_handle_irq(vcpu);
 	local_irq_enable();
 
 	trace_kvm_exit(vcpu, ecode);

base-commit: 2408a807bfc3f738850ef5ad5e3fd59d66168996
-- 
2.39.3