Re: [PATCH v2 01/17] KVM: arm64: Factor out stage 2 page table data from struct kvm

Marc Zyngier
2020-07-13T14:20:37Z

On Mon, 13 Jul 2020 10:47:49 +0100,
Andrew Scull <ascull@google.com> wrote:
>
> On Mon, Jun 15, 2020 at 02:27:03PM +0100, Marc Zyngier wrote:
> > -static void __hyp_text __tlb_switch_to_guest_nvhe(struct kvm *kvm,
> > +static void __hyp_text __tlb_switch_to_guest_nvhe(struct kvm_s2_mmu *mmu,
> > struct tlb_inv_context *cxt)
> > {
> > if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
> > @@ -79,22 +79,19 @@ static void __hyp_text __tlb_switch_to_guest_nvhe(struct kvm *kvm,
> > isb();
> > }
> >
> > - /* __load_guest_stage2() includes an ISB for the workaround. */
> > - __load_guest_stage2(kvm);
> > - asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
> > + __load_guest_stage2(mmu);
> > }
>
> Just noticed that this drops the ISB when the speculative AT workaround
> is not active.
>
> This alternative is 'backwards' to avoid a double ISB as there is one in
> __load_guest_stage2 when the workaround is active. I hope to address
> this smell in an upcoming series but, for now, we should at least have
> an ISB.

Indeed. I must have messed up a conflict resolution here. I'll stick
this fix on top.

Thanks,

M.

From 997c17ffe879dcad40b49a0c844c39f5d071dee9 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@kernel.org>
Date: Mon, 13 Jul 2020 15:15:14 +0100
Subject: [PATCH] KVM: arm64: Restore missing ISB on nVHE __tlb_switch_to_guest

Commit a0e50aa3f4a8 ("KVM: arm64: Factor out stage 2 page table
data from struct kvm") dropped the ISB after __load_guest_stage2(),
only leaving the one that is required when the speculative AT
workaround is in effect.

As Andrew points it: "This alternative is 'backwards' to avoid a
double ISB as there is one in __load_guest_stage2 when the workaround
is active."

Restore the missing ISB, conditionned on the AT workaround not being
active.

Fixes: a0e50aa3f4a8 ("KVM: arm64: Factor out stage 2 page table data from struct kvm")
Reported-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/hyp/nvhe/tlb.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/tlb.c b/arch/arm64/kvm/hyp/nvhe/tlb.c
index 69eae608d670..f31185272b50 100644
--- a/arch/arm64/kvm/hyp/nvhe/tlb.c
+++ b/arch/arm64/kvm/hyp/nvhe/tlb.c
@@ -31,7 +31,9 @@ static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
isb();
}

+ /* __load_guest_stage2() includes an ISB for the workaround. */
__load_guest_stage2(mmu);
+ asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
}

static void __tlb_switch_to_host(struct tlb_inv_context *cxt)
--
2.27.0

--
Without deviation from the norm, progress is not possible.