linux-kernel - [PATCH 4.19 274/280] KVM: x86/mmu: Detect MMIO generation wrap in any address space

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Date:   Fri, 22 Mar 2019 12:17:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 4.19 274/280] KVM: x86/mmu: Detect MMIO generation wrap in any address space

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sean Christopherson <sean.j.christopherson@...el.com>

commit e1359e2beb8b0a1188abc997273acbaedc8ee791 upstream.

The check to detect a wrap of the MMIO generation explicitly looks for a
generation number of zero.  Now that unique memslots generation numbers
are assigned to each address space, only address space 0 will get a
generation number of exactly zero when wrapping.  E.g. when address
space 1 goes from 0x7fffe to 0x80002, the MMIO generation number will
wrap to 0x2.  Adjust the MMIO generation to strip the address space
modifier prior to checking for a wrap.

Fixes: 4bd518f1598d ("KVM: use separate generations for each address space")
Cc: <stable@...r.kernel.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/mmu.c |   21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5776,11 +5776,28 @@ static bool kvm_has_zapped_obsolete_page
 
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
 {
+	gen &= MMIO_GEN_MASK;
+
+	/*
+	 * Shift to eliminate the "update in-progress" flag, which isn't
+	 * included in the spte's generation number.
+	 */
+	gen >>= 1;
+
+	/*
+	 * Generation numbers are incremented in multiples of the number of
+	 * address spaces in order to provide unique generations across all
+	 * address spaces.  Strip what is effectively the address space
+	 * modifier prior to checking for a wrap of the MMIO generation so
+	 * that a wrap in any address space is detected.
+	 */
+	gen &= ~((u64)KVM_ADDRESS_SPACE_NUM - 1);
+
 	/*
-	 * The very rare case: if the generation-number is round,
+	 * The very rare case: if the MMIO generation number has wrapped,
 	 * zap all shadow pages.
 	 */
-	if (unlikely((gen & MMIO_GEN_MASK) == 0)) {
+	if (unlikely(gen == 0)) {
 		kvm_debug_ratelimited("kvm: zapping shadow pages for mmio generation wraparound\n");
 		kvm_mmu_invalidate_zap_all_pages(kvm);
 	}