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Message-ID: <YW6SiMLU19YN1ARe@google.com>
Date: Tue, 19 Oct 2021 10:40:24 +0100
From: Quentin Perret <qperret@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: James Morse <james.morse@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Fuad Tabba <tabba@...gle.com>,
David Brazdil <dbrazdil@...gle.com>,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 16/16] KVM: arm64: pkvm: Unshare guest structs during
teardown
On Monday 18 Oct 2021 at 18:12:22 (+0100), Marc Zyngier wrote:
> On 2021-10-18 15:03, Quentin Perret wrote:
> > On Monday 18 Oct 2021 at 11:32:13 (+0100), Quentin Perret wrote:
> > > Another option is to take a refcount on 'current' from
> > > kvm_arch_vcpu_run_map_fp() before sharing thread-specific structs with
> > > the hyp and release the refcount of the previous task after unsharing.
> > > But that means we'll have to also drop the refcount when the vcpu
> > > gets destroyed, as well as explicitly unshare at that point. Shouldn't
> > > be too bad I think. Thoughts?
> >
> > Something like the below seems to work OK on my setup, including
> > SIGKILL'ing the guest and such. How much do you hate it?
>
> It is annoyingly elegant! Small nitpick below.
>
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h
> > b/arch/arm64/include/asm/kvm_host.h
> > index f8be56d5342b..50598d704c71 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -322,6 +322,7 @@ struct kvm_vcpu_arch {
> >
> > struct thread_info *host_thread_info; /* hyp VA */
> > struct user_fpsimd_state *host_fpsimd_state; /* hyp VA */
> > + struct task_struct *parent_task;
> >
> > struct {
> > /* {Break,watch}point registers */
> > @@ -738,6 +739,7 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
> > void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu);
> > void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu);
> > void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu);
> > +void kvm_vcpu_unshare_task_fp(struct kvm_vcpu *vcpu);
> >
> > static inline bool kvm_pmu_counter_deferred(struct perf_event_attr
> > *attr)
> > {
> > diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> > index 2fe1128d9f3d..27afeebbe1cb 100644
> > --- a/arch/arm64/kvm/fpsimd.c
> > +++ b/arch/arm64/kvm/fpsimd.c
> > @@ -15,6 +15,22 @@
> > #include <asm/kvm_mmu.h>
> > #include <asm/sysreg.h>
> >
> > +void kvm_vcpu_unshare_task_fp(struct kvm_vcpu *vcpu)
> > +{
> > + struct task_struct *p = vcpu->arch.parent_task;
> > + struct user_fpsimd_state *fpsimd;
> > + struct thread_info *ti;
> > +
> > + if (!static_branch_likely(&kvm_protected_mode_initialized) || !p)
>
> Shouldn't this be a check on is_protected_kvm_enabled() instead?
> The two should be equivalent outside of the initialisation code...
Yup, it'd be nice to do checks on kvm_protected_mode_initialized only
when they're strictly necessary, and that's not the case here. I'll fold
that change in v2.
Cheers
Quentin
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