linux-kernel - Re: [PATCH] iommu/amd: fix interrupt remapping for avic

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Message-ID: <41a32d50-63ae-a8f3-bc2e-eee28e9e1c08@amd.com>
Date:   Wed, 16 Sep 2020 17:38:09 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Joao Martins <joao.m.martins@...cle.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        "Grimm, Jon" <jon.grimm@....com>
Subject: Re: [PATCH] iommu/amd: fix interrupt remapping for avic



On 9/15/20 8:19 PM, Joao Martins wrote:
> On 9/15/20 1:30 PM, Suravee Suthikulpanit wrote:
>> On 9/15/20 6:25 PM, Maxim Levitsky wrote:
>>> On Mon, 2020-09-14 at 21:48 +0700, Suravee Suthikulpanit wrote:
>>>> Could you please try with the following patch instead?
>>>>
>>>> --- a/drivers/iommu/amd/iommu.c
>>>> +++ b/drivers/iommu/amd/iommu.c
>>>> @@ -3840,14 +3840,18 @@ int amd_iommu_activate_guest_mode(void *data)
>>>>     {
>>>>            struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
>>>>            struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
>>>> +       u64 valid;
>>>>
>>>>            if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
>>>>                !entry || entry->lo.fields_vapic.guest_mode)
>>>>                    return 0;
>>>>
>>>> +       valid = entry->lo.fields_vapic.valid;
>>>> +
>>>>            entry->lo.val = 0;
>>>>            entry->hi.val = 0;
>>>>
>>>> +       entry->lo.fields_vapic.valid       = valid;
>>>>            entry->lo.fields_vapic.guest_mode  = 1;
>>>>            entry->lo.fields_vapic.ga_log_intr = 1;
>>>>            entry->hi.fields.ga_root_ptr       = ir_data->ga_root_ptr;
>>>> @@ -3864,12 +3868,14 @@ int amd_iommu_deactivate_guest_mode(void *data)
>>>>            struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
>>>>            struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
>>>>            struct irq_cfg *cfg = ir_data->cfg;
>>>> -       u64 valid = entry->lo.fields_remap.valid;
>>>> +       u64 valid;
>>>>
>>>>            if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
>>>>                !entry || !entry->lo.fields_vapic.guest_mode)
>>>>                    return 0;
>>>>
>>>> +       valid = entry->lo.fields_remap.valid;
>>>> +
>>>>            entry->lo.val = 0;
>>>>            entry->hi.val = 0;
>>> I see. I based my approach on the fact that valid bit was
>>> set always to true anyway before, plus that amd_iommu_activate_guest_mode
>>> should be really only called when someone activates a valid interrupt remapping
>>> entry, but IMHO the approach of preserving the valid bit is safer anyway.
>>>
>>> It works on my system (I applied the patch manually, since either your or my email client,
>>> seems to mangle the patch)
>>>
>>
>> Sorry for the mangled patch. I'll submit the patch w/ your information. Thanks for your help reporting, debugging, and
>> testing the patch.
>>
> I assume you're only doing the valid bit preservation in amd_iommu_activate_guest_mode() ?
> The null deref fix in amd_iommu_deactivate_guest_mode() was fixed elsewhere[0], or are you
> planning on merging both changes like the diff you attached?

I am planning to send a separate patch just for amd_iommu_activate_guest_mode().

> Asking also because commit 26e495f341 ("iommu/amd: Restore IRTE.RemapEn bit after
> programming IRTE") was added in v5.4 and v5.8 stable trees but the v5.4 backport didn't
> include e52d58d54a321 ("iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE").

We should probably backport the e52d58d54a321 along with the fixes in amd_iommu_activate_guest_mode() and 
amd_iommu_deactivate_guest_mode(). I'll work with the community to get these back-ported.

Thanks,
Suravee