Re: [PATCH v4 5/5] iommu/arm-smmu-v3: add bootup option "arm_iommu"

From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: Robin Murphy <robin.murphy@arm.com>,
	Will Deacon <will.deacon@arm.com>, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	iommu <iommu@lists.linux-foundation.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Cc: LinuxArm <linuxarm@huawei.com>, Hanjun Guo <guohanjun@huawei.com>,
	Libin <huawei.libin@huawei.com>
Subject: Re: [PATCH v4 5/5] iommu/arm-smmu-v3: add bootup option "arm_iommu"
Date: Mon, 13 Aug 2018 15:50:17 +0800	[thread overview]
Message-ID: <5B713839.1010609@huawei.com> (raw)
In-Reply-To: <c46fa263-2dfa-b8fc-b2c1-0b1bf6029748@arm.com>

On 2018/8/9 19:08, Robin Murphy wrote:
> On 06/08/18 13:27, Zhen Lei wrote:
>> Add a bootup option to make the system manager can choose which mode to
>> be used. The default mode is strict.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>>   Documentation/admin-guide/kernel-parameters.txt |  9 +++++++++
>>   drivers/iommu/arm-smmu-v3.c                     | 17 ++++++++++++++++-
>>   2 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 533ff5c..426e989 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1720,6 +1720,15 @@
>>           nobypass    [PPC/POWERNV]
>>               Disable IOMMU bypass, using IOMMU for PCI devices.
>>
>> +    arm_iommu=    [ARM64]
>> +        non-strict    [Default Off]
> 
> Again, I'd much rather have "iommu.non_strict= { "0" | "1" }" in line with the passthrough option.

OK，I will change it in the next version.

> 
> Robin.
> 
>> +            Put off TLBs invalidation and release memory first.
>> +            It's good for scatter-gather performance but lacks full
>> +            isolation, an untrusted device can access the reused
>> +            memory because the TLBs may still valid. Please take
>> +            full consideration before choosing this mode.
>> +            Note that, VFIO will always use strict mode.
>> +
>>       iommu.passthrough=
>>               [ARM64] Configure DMA to bypass the IOMMU by default.
>>               Format: { "0" | "1" }
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index 904bc1e..9a30892 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -631,6 +631,21 @@ struct arm_smmu_option_prop {
>>       { 0, NULL},
>>   };
>>
>> +static u32 smmu_non_strict __read_mostly;
>> +
>> +static int __init arm_smmu_setup(char *str)
>> +{
>> +    if (!strncmp(str, "non-strict", 10)) {
>> +        smmu_non_strict = 1;
>> +        pr_warn("WARNING: iommu non-strict mode is chosen.\n"
>> +            "It's good for scatter-gather performance but lacks full isolation\n");
>> +        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
>> +    }
>> +
>> +    return 0;
>> +}
>> +early_param("arm_iommu", arm_smmu_setup);
>> +
>>   static inline void __iomem *arm_smmu_page1_fixup(unsigned long offset,
>>                            struct arm_smmu_device *smmu)
>>   {
>> @@ -1622,7 +1637,7 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
>>       if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
>>           pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
>>
>> -    if (domain->type == IOMMU_DOMAIN_DMA) {
>> +    if ((domain->type == IOMMU_DOMAIN_DMA) && smmu_non_strict) {
>>           domain->non_strict = 1;
>>           pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>>       }
>> -- 
>> 1.8.3
>>
>>
> 
> .
> 

-- 
Thanks!
BestRegards