linux-kernel - Re: [PATCH] KVM: x86/xen: Fix SRCU/RCU usage in readers of evtchn

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Date:   Sat, 24 Dec 2022 10:54:14 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     paul@....org, seanjc@...gle.com, Michal Luczaj <mhal@...x.co>
Subject: Re: [PATCH] KVM: x86/xen: Fix SRCU/RCU usage in readers of
 evtchn_ports

On Sat, 2022-12-24 at 03:53 -0500, Paolo Bonzini wrote:
> @@ -2005,19 +2009,23 @@ static bool kvm_xen_hcall_evtchn_send(struct
> kvm_vcpu *vcpu, u64 param, u64 *r)
>         gpa_t gpa;
>         int idx;
>  
> +       /*
> +        * evtchnfd is protected by kvm->srcu; the idr lookup instead
> +        * is protected by RCU.
> +        */
>         idx = srcu_read_lock(&vcpu->kvm->srcu);
>         gpa = kvm_mmu_gva_to_gpa_system(vcpu, param, NULL);
> -       srcu_read_unlock(&vcpu->kvm->srcu, idx);
>  

I removed that srcu_read_lock() in
https://lore.kernel.org/kvm/d52040a8d46e68efd86273be66808fe4a8c70e1d.camel@infradead.org/
on the basis that this is a hypercall handler, called from the
handle_exit function, with the lock already taken.

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