linux-kernel - Re: [PATCH 06/67] iommu/amd: WARN if KVM attempts to set vCPU affinity without posted intrrupts

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1b29eed0-fafc-427b-bd70-5dd087f2c0dd@redhat.com>
Date: Tue, 15 Apr 2025 13:42:33 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Sairaj Kodilkar <sarunkod@....com>
Cc: Joerg Roedel <joro@...tes.org>, David Woodhouse <dwmw2@...radead.org>,
 Lu Baolu <baolu.lu@...ux.intel.com>, kvm@...r.kernel.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Maxim Levitsky <mlevitsk@...hat.com>,
 Joao Martins <joao.m.martins@...cle.com>, David Matlack
 <dmatlack@...gle.com>, Naveen N Rao <naveen.rao@....com>,
 Vasant Hegde <vasant.hegde@....com>
Subject: Re: [PATCH 06/67] iommu/amd: WARN if KVM attempts to set vCPU
 affinity without posted intrrupts

On 4/11/25 16:10, Sean Christopherson wrote:
> On Fri, Apr 11, 2025, Sairaj Kodilkar wrote:
>> On 4/5/2025 1:08 AM, Sean Christopherson wrote:
>>> WARN if KVM attempts to set vCPU affinity when posted interrupts aren't
>>> enabled, as KVM shouldn't try to enable posting when they're unsupported,
>>> and the IOMMU driver darn well should only advertise posting support when
>>> AMD_IOMMU_GUEST_IR_VAPIC() is true.
>>>
>>> Note, KVM consumes is_guest_mode only on success.
>>>
>>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>>> ---
>>>    drivers/iommu/amd/iommu.c | 13 +++----------
>>>    1 file changed, 3 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
>>> index b3a01b7757ee..4f69a37cf143 100644
>>> --- a/drivers/iommu/amd/iommu.c
>>> +++ b/drivers/iommu/amd/iommu.c
>>> @@ -3852,19 +3852,12 @@ static int amd_ir_set_vcpu_affinity(struct irq_data *data, void *vcpu_info)
>>>    	if (!dev_data || !dev_data->use_vapic)
>>>    		return -EINVAL;
>>> +	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
>>> +		return -EINVAL;
>>> +
>>
>> Hi Sean,
>> 'dev_data->use_vapic' is always zero when AMD IOMMU uses legacy
>> interrupts i.e. when AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) is 0.
>> Hence you can remove this additional check.
> 
> Hmm, or move it above?  KVM should never call amd_ir_set_vcpu_affinity() if
> IRQ posting is unsupported, and that would make this consistent with the end
> behavior of amd_iommu_update_ga() and amd_iommu_{de,}activate_guest_mode().
> 
> 	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
> 		return -EINVAL;
> 
> 	if (ir_data->iommu == NULL)
> 		return -EINVAL;
> 
> 	dev_data = search_dev_data(ir_data->iommu, irte_info->devid);
> 
> 	/* Note:
> 	 * This device has never been set up for guest mode.
> 	 * we should not modify the IRTE
> 	 */
> 	if (!dev_data || !dev_data->use_vapic)
> 		return -EINVAL;
> 
> I'd like to keep the WARN so that someone will notice if KVM screws up.

Makes sense, avic_pi_update_irte() returns way before it has the 
occasion to call irq_set_vcpu_affinity().

Paolo