linux-kernel - [PATCH] kvm: x86: Do not handle MMIO request in fast_page

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Date:   Tue,  5 Sep 2017 17:29:41 +0800
From:   changbin.du@...el.com
To:     pbonzini@...hat.com, rkrcmar@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Changbin Du <changbin.du@...mail.com>,
        Changbin Du <changbin.du@...el.com>
Subject: [PATCH] kvm: x86: Do not handle MMIO request in fast_page_fault

From: Changbin Du <changbin.du@...mail.com>

If it is a MMIO request, it should be handled by slow path. This patch
actually fixed below warning when mmu debug is enabled.

WARNING: CPU: 5 PID: 2282 at arch/x86/kvm/mmu.c:226 fast_page_fault+0x41b/0x520
CPU: 5 PID: 2282 Comm: qemu-system-x86 Not tainted 4.13.0-rc6+ #34
task: ffff9b47f5286000 task.stack: ffffb18d03b28000
RIP: 0010:fast_page_fault+0x41b/0x520
Call Trace:
  tdp_page_fault+0xfb/0x290
  kvm_mmu_page_fault+0x61/0x120
  handle_ept_misconfig+0x1ba/0x1c0
  vmx_handle_exit+0xb8/0xd70
  ? kvm_arch_vcpu_ioctl_run+0x9b6/0x18e0
  kvm_arch_vcpu_ioctl_run+0xa5a/0x18e0
  ? kvm_arch_vcpu_load+0x62/0x230
  kvm_vcpu_ioctl+0x340/0x6c0
  ? kvm_vcpu_ioctl+0x340/0x6c0
  ? lock_acquire+0xf5/0x1f0
  do_vfs_ioctl+0xa2/0x670
  ? __fget+0x107/0x200
  SyS_ioctl+0x79/0x90
  entry_SYSCALL_64_fastpath+0x23/0xc2

Signed-off-by: Changbin Du <changbin.du@...mail.com>
Signed-off-by: Changbin Du <changbin.du@...el.com>
---
 arch/x86/kvm/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9d3f275..d6b2b27 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3201,7 +3201,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 
 		new_spte = spte;
 
-		if (is_access_track_spte(spte))
+		if (!is_mmio_spte(spte) && is_access_track_spte(spte))
 			new_spte = restore_acc_track_spte(new_spte);
 
 		/*
-- 
2.7.4