linux-kernel - Re: [RFC PATCH 6/6] iommu/arm-smmu-v3: Avoid ILLEGAL setting of STE.S1STALLD and CD.S

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Message-ID: <e214b851-efa8-a45f-7deb-b99f3873564b@arm.com>
Date:   Wed, 13 Sep 2017 16:47:27 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Yisheng Xie <xieyisheng1@...wei.com>,
        Will Deacon <Will.Deacon@....com>
Cc:     "joro@...tes.org" <joro@...tes.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        "hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
        Sudeep Holla <Sudeep.Holla@....com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "lenb@...nel.org" <lenb@...nel.org>,
        Robin Murphy <Robin.Murphy@....com>,
        "robert.moore@...el.com" <robert.moore@...el.com>,
        "lv.zheng@...el.com" <lv.zheng@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devel@...ica.org" <devel@...ica.org>,
        "liubo95@...wei.com" <liubo95@...wei.com>,
        "chenjiankang1@...wei.com" <chenjiankang1@...wei.com>
Subject: Re: [RFC PATCH 6/6] iommu/arm-smmu-v3: Avoid ILLEGAL setting of
 STE.S1STALLD and CD.S

On 13/09/17 11:11, Yisheng Xie wrote:
> Hi Will,
> 
> On 2017/9/13 11:06, Will Deacon wrote:
>> On Tue, Sep 05, 2017 at 01:54:19PM +0100, Jean-Philippe Brucker wrote:
>>> On 31/08/17 09:20, Yisheng Xie wrote:
>>>> It is ILLEGAL to set STE.S1STALLD if STALL_MODEL is not 0b00, which
>>>> means we should not disable stall mode if stall/terminate mode is not
>>>> configuable.
>>>>
>>>> Meanwhile, it is also ILLEGAL when STALL_MODEL==0b10 && CD.S==0 which
>>>> means if stall mode is force we should always set CD.S.
>>>>
>>>> This patch add ARM_SMMU_FEAT_TERMINATE feature bit for smmu, and use
>>>> TERMINATE feature checking to ensue above ILLEGAL cases from happening.
>>>>
>>>> Signed-off-by: Yisheng Xie <xieyisheng1@...wei.com>
>>>> ---
>>>>  drivers/iommu/arm-smmu-v3.c | 22 ++++++++++++++++------
>>>>  1 file changed, 16 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>>>> index dbda2eb..0745522 100644
>>>> --- a/drivers/iommu/arm-smmu-v3.c
>>>> +++ b/drivers/iommu/arm-smmu-v3.c
>>>> @@ -55,6 +55,7 @@
>>>>  #define IDR0_STALL_MODEL_SHIFT             24
>>>>  #define IDR0_STALL_MODEL_MASK              0x3
>>>>  #define IDR0_STALL_MODEL_STALL             (0 << IDR0_STALL_MODEL_SHIFT)
>>>> +#define IDR0_STALL_MODEL_NS                (1 << IDR0_STALL_MODEL_SHIFT)
>>>>  #define IDR0_STALL_MODEL_FORCE             (2 << IDR0_STALL_MODEL_SHIFT)
>>>>  #define IDR0_TTENDIAN_SHIFT                21
>>>>  #define IDR0_TTENDIAN_MASK         0x3
>>>> @@ -766,6 +767,7 @@ struct arm_smmu_device {
>>>>  #define ARM_SMMU_FEAT_SVM          (1 << 15)
>>>>  #define ARM_SMMU_FEAT_HA           (1 << 16)
>>>>  #define ARM_SMMU_FEAT_HD           (1 << 17)
>>>> +#define ARM_SMMU_FEAT_TERMINATE            (1 << 18)
>>>
>>> I'd rather introduce something like "ARM_SMMU_FEAT_STALL_FORCE" instead.
>>> Terminate model has another meaning, and is defined by a different bit in
>>> IDR0.
>> 
>> Yes. What we need to do is:
>> 
>> - If STALL_MODEL is 0b00, then set S1STALLD
> 
> Yes, and within this case, we can only set the S1STALLD for masters which can
> not stall in the future?
> 
>> - If STALL_MODEL is 0b01, then we're ok (in future, avoiding trying to use
>>   stalls, even for masters that claim to support it)
>> - If STALL_MODEL is 0b10, then force all PCI devices and any platform
>>   devices that don't claim to support stalls into bypass (depending on
>>   disable_bypass).
>> 
>> Reasonable? We could actually knock up a fix for mainline to do most of
>> this already.
> This sound reasonable to me. And I can be a volunteer to prepare this patch if
> Jean-Philippe do not oppose :)

Sure go ahead, I'll rebase the platform SVM work on top of it.

Thanks,
Jean