linux-kernel - [PATCH 1/5] KVM: x86/mmu: Don't attempt to map leaf if target TDP MMU SPTE is frozen

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Date:   Tue, 13 Dec 2022 03:30:26 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Robert Hoo <robert.hu@...ux.intel.com>,
        Greg Thelen <gthelen@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH 1/5] KVM: x86/mmu: Don't attempt to map leaf if target TDP MMU
 SPTE is frozen

Hoist the is_removed_spte() check above the "level == goal_level" check
when walking SPTEs during a TDP MMU page fault to avoid attempting to map
a leaf entry if said entry is frozen by a different task/vCPU.

  ------------[ cut here ]------------
  WARNING: CPU: 3 PID: 939 at arch/x86/kvm/mmu/tdp_mmu.c:653 kvm_tdp_mmu_map+0x269/0x4b0
  Modules linked in: kvm_intel
  CPU: 3 PID: 939 Comm: nx_huge_pages_t Not tainted 6.1.0-rc4+ #67
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:kvm_tdp_mmu_map+0x269/0x4b0
  RSP: 0018:ffffc9000068fba8 EFLAGS: 00010246
  RAX: 00000000000005a0 RBX: ffffc9000068fcc0 RCX: 0000000000000005
  RDX: ffff88810741f000 RSI: ffff888107f04600 RDI: ffffc900006a3000
  RBP: 060000010b000bf3 R08: 0000000000000000 R09: 0000000000000000
  R10: 0000000000000000 R11: 000ffffffffff000 R12: 0000000000000005
  R13: ffff888113670000 R14: ffff888107464958 R15: 0000000000000000
  FS:  00007f01c942c740(0000) GS:ffff888277cc0000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 0000000117013006 CR4: 0000000000172ea0
  Call Trace:
   <TASK>
   kvm_tdp_page_fault+0x10c/0x130
   kvm_mmu_page_fault+0x103/0x680
   vmx_handle_exit+0x132/0x5a0 [kvm_intel]
   vcpu_enter_guest+0x60c/0x16f0
   kvm_arch_vcpu_ioctl_run+0x1e2/0x9d0
   kvm_vcpu_ioctl+0x271/0x660
   __x64_sys_ioctl+0x80/0xb0
   do_syscall_64+0x2b/0x50
   entry_SYSCALL_64_after_hwframe+0x46/0xb0
   </TASK>
  ---[ end trace 0000000000000000 ]---

Fixes: 63d28a25e04c ("KVM: x86/mmu: simplify kvm_tdp_mmu_map flow when guest has to retry")
Cc: Robert Hoo <robert.hu@...ux.intel.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 764f7c87286f..b740f38fedcc 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1162,9 +1162,6 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		if (fault->nx_huge_page_workaround_enabled)
 			disallowed_hugepage_adjust(fault, iter.old_spte, iter.level);
 
-		if (iter.level == fault->goal_level)
-			break;
-
 		/*
 		 * If SPTE has been frozen by another thread, just give up and
 		 * retry, avoiding unnecessary page table allocation and free.
@@ -1172,6 +1169,9 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		if (is_removed_spte(iter.old_spte))
 			goto retry;
 
+		if (iter.level == fault->goal_level)
+			break;
+
 		/* Step down into the lower level page table if it exists. */
 		if (is_shadow_present_pte(iter.old_spte) &&
 		    !is_large_pte(iter.old_spte))
-- 
2.39.0.rc1.256.g54fd8350bd-goog