From: Will Deacon <will@kernel.org>
To: kvmarm@lists.cs.columbia.edu
Cc: kernel-team@android.com, Marc Zyngier <maz@kernel.org>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: [PATCH 7/7] KVM: arm64: Separate write faults on read-only memslots from MMIO
Date: Fri, 24 Jul 2020 15:35:06 +0100 [thread overview]
Message-ID: <20200724143506.17772-8-will@kernel.org> (raw)
In-Reply-To: <20200724143506.17772-1-will@kernel.org>
Although taking a write-fault on a read-only memslot triggers an MMIO
exit back to userspace, lumping the handling together in
kvm_handle_guest_abort() causes some of the early triage to have weird
effects on userspace. For example, if a guest generates a stage-2 fault
on a stage-1 translation fault when trying to fetch an instruction from
a read-only memslot, it will be mistakenly treated as an attempt to
execute from MMIO and a prefetch abort will be re-injected into the
guest.
Separate the MMIO handling from the read-only memslot handling, so that
the latter is left entirely up to userspace. Note that this _will_
result in more exits than before for read-only memslots, since userspace
will now see some cache maintenance and instruction-side aborts.
Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/kvm/mmu.c | 45 ++++++++++++++++++++++++--------------------
1 file changed, 25 insertions(+), 20 deletions(-)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 9e72e7f4a2c2..2edc6f2412dc 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2117,9 +2117,30 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
memslot = gfn_to_memslot(vcpu->kvm, gfn);
hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
write_fault = kvm_is_write_fault(vcpu);
- if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
+
+ /*
+ * The IPA is reported as [MAX:12], so we need to complement it with
+ * the bottom 12 bits from the faulting VA. This is always 12 bits,
+ * irrespective of the page size.
+ */
+ fault_ipa |= kvm_vcpu_get_hfar(vcpu) & ((1 << 12) - 1);
+
+ /*
+ * We can perform some early fault triage based purely on the memslot
+ * information:
+ *
+ * Faults on IPAs falling outside of any memslot are re-injected
+ * into the guest as external aborts if they were either signalled as
+ * instruction aborts or as a stage-2 fault on a translation table walk.
+ * If the instruction was a cache maintenance instruction then it is
+ * quietly skipped, otherwise we exit to userspace for MMIO emulation.
+ *
+ * Write faults on IPAs falling within a read-only memslot are reported
+ * to userspace as MMIO exits. This includes cache maintenance and
+ * stage-2 faults on translation table walks,
+ */
+ if (kvm_is_error_hva(hva)) {
if (kvm_vcpu_trap_is_iabt(vcpu)) {
- /* Prefetch Abort on I/O address */
ret = -ENOEXEC;
goto out;
}
@@ -2129,30 +2150,12 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
goto out;
}
- /*
- * Check for a cache maintenance operation. Since we
- * ended-up here, we know it is outside of any memory
- * slot. But we can't find out if that is for a device,
- * or if the guest is just being stupid. The only thing
- * we know for sure is that this range cannot be cached.
- *
- * So let's assume that the guest is just being
- * cautious, and skip the instruction.
- */
if (kvm_vcpu_dabt_is_cm(vcpu)) {
kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
ret = 1;
goto out_unlock;
}
- /*
- * The IPA is reported as [MAX:12], so we need to
- * complement it with the bottom 12 bits from the
- * faulting VA. This is always 12 bits, irrespective
- * of the page size.
- */
- fault_ipa |= kvm_vcpu_get_hfar(vcpu) & ((1 << 12) - 1);
-
/*
* No valid syndrome? Ask userspace for help if it has
* volunteered to do so, and bail out otherwise.
@@ -2161,7 +2164,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
ret = handle_error_invalid_dabt(vcpu, run, fault_ipa);
goto out_unlock;
}
+ }
+ if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
ret = io_mem_abort(vcpu, run, fault_ipa);
goto out_unlock;
}
--
2.28.0.rc0.142.g3c755180ce-goog
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prev parent reply other threads:[~2020-07-24 14:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-24 14:34 [PATCH 0/7] KVM: arm64: Fixes to early stage-2 fault handling Will Deacon
2020-07-24 14:35 ` [PATCH 1/7] KVM: arm64: Update comment when skipping guest MMIO access instruction Will Deacon
2020-07-26 11:08 ` Marc Zyngier
2020-07-27 10:30 ` Will Deacon
2020-07-24 14:35 ` [PATCH 2/7] KVM: arm64: Rename kvm_vcpu_dabt_isextabt() Will Deacon
2020-07-26 11:15 ` Marc Zyngier
2020-07-27 10:30 ` Will Deacon
2020-07-24 14:35 ` [PATCH 3/7] KVM: arm64: Handle data and instruction external aborts the same way Will Deacon
2020-07-24 14:35 ` [PATCH 4/7] KVM: arm64: Remove useless local variable Will Deacon
2020-07-24 14:35 ` [PATCH 5/7] KVM: arm64: Move 'invalid syndrome' logic out of io_mem_abort() Will Deacon
2020-07-26 11:55 ` Marc Zyngier
2020-07-27 10:31 ` Will Deacon
2020-07-24 14:35 ` [PATCH 6/7] KVM: arm64: Handle stage-2 faults on stage-1 page-table walks earlier Will Deacon
2020-07-26 13:38 ` Marc Zyngier
2020-07-27 10:29 ` Will Deacon
2020-07-24 14:35 ` Will Deacon [this message]
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