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Subject: Re: [PATCH 1/2] KVM: VMX: Disable posted interrupts for odd IRQs
From:   Liran Alon <liran.alon@oracle.com>
In-Reply-To: <20190903142954.3429-2-graf@amazon.com>
Date:   Wed, 4 Sep 2019 02:15:23 +0300
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Joerg Roedel <joro@8bytes.org>,
        Jim Mattson <jmattson@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        =?utf-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>
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References: <20190903142954.3429-1-graf@amazon.com>
 <20190903142954.3429-2-graf@amazon.com>
To:     Alexander Graf <graf@amazon.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On 3 Sep 2019, at 17:29, Alexander Graf <graf@amazon.com> wrote:
>=20
> We can easily route hardware interrupts directly into VM context when
> they target the "Fixed" or "LowPriority" delivery modes.
>=20
> However, on modes such as "SMI" or "Init", we need to go via KVM code
> to actually put the vCPU into a different mode of operation, so we can
> not post the interrupt

I would also mention in commit message that one can see this is also
true in KVM=E2=80=99s vLAPIC code. i.e. __apic_accept_irq() can call
kvm_x86_ops->deliver_posted_interrupt() only in case deliver-mode is
either =E2=80=9CFixed=E2=80=9D or =E2=80=9CLowPriority=E2=80=9D.=20

>=20
> Add code in the VMX PI logic to explicitly refuse to establish posted
> mappings for advanced IRQ deliver modes.
>=20
> This fixes a bug I have with code which configures real hardware to
> inject virtual SMIs into my guest.
>=20
> Signed-off-by: Alexander Graf <graf@amazon.com>

With some small improvements I written inline below:
Reviewed-by: Liran Alon <liran.alon@oracle.com>

> ---
> arch/x86/kvm/vmx/vmx.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>=20
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 570a233e272b..d16c4ae8f685 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7401,6 +7401,28 @@ static int vmx_update_pi_irte(struct kvm *kvm, =
unsigned int host_irq,
> 			continue;
> 		}
>=20
> +		switch (irq.delivery_mode) {
> +		case dest_Fixed:
> +		case dest_LowestPrio:
> +			break;
> +		default:
> +			/*
> +			 * For non-trivial interrupt events, we need to =
go
> +			 * through the full KVM IRQ code, so refuse to =
take
> +			 * any direct PI assignments here.
> +			 */
> +
> +			ret =3D irq_set_vcpu_affinity(host_irq, NULL);
> +			if (ret < 0) {
> +				printk(KERN_INFO
> +				   "failed to back to remapped mode, =
irq: %u\n",
> +				   host_irq);
> +				goto out;

I recommend we will chose to print here a string that is different than =
the !kvm_intr_is_single_vcpu()
case to make it easier to diagnose which case exactly failed.

-Liran

> +			}
> +
> +			continue;
> +		}
> +
> 		vcpu_info.pi_desc_addr =3D __pa(vcpu_to_pi_desc(vcpu));
> 		vcpu_info.vector =3D irq.vector;
>=20
> --=20
> 2.17.1
>=20
>=20
>=20
>=20
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> Krausenstr. 38
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>=20
>=20
>=20