| Message ID | 20220802234207.1994093-1-ishii.shuuichir@fujitsu.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iommu/arm-smmu-v3: fixed check process for disable_bypass module parameter | expand |
On 2022-08-03 00:42, Shuuichirou Ishii wrote: > The current process does not enable the bypass setting regardless of > the value of the disable_bypass module parameter when ACPI is enabled, > so the value of the disable_bypass module parameter has been corrected > so that it is handled correctly. > > Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@fujitsu.com> > --- > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > index 88817a3376ef..256d7b2a83a7 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -3396,7 +3396,7 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass) > enables &= ~(CR0_EVTQEN | CR0_PRIQEN); > > /* Enable the SMMU interface, or ensure bypass */ > - if (!bypass || disable_bypass) { > + if (!bypass && disable_bypass) { This change looks obviously wrong - if bypass is false here then we definitely want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be possible to get here with bypass==true under ACPI, since arm_smmu_device_acpi_probe() cannot fail :/ Robin. > enables |= CR0_SMMUEN; > } else { > ret = arm_smmu_update_gbpa(smmu, 0, GBPA_ABORT);
Hi, Robin, Thank you for your comments. > > /* Enable the SMMU interface, or ensure bypass */ > > - if (!bypass || disable_bypass) { > > + if (!bypass && disable_bypass) { > > This change looks obviously wrong - if bypass is false here then we definitely > want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be > possible to get here with bypass==true under ACPI, since > arm_smmu_device_acpi_probe() cannot fail :/ Sorry, my understanding of the meaning of the disable_bypass module parameter and the process of setting GBPA_ABORT was insufficient. I misunderstood that the disable_bypass module parameter is used to simply bypass (disable) SMMU (SMMU_CR0.SMMUEN == 0 and SMMU_GBPA.ABORT == 0). Forget about the fixes in this patch. Although our understanding was lacking, we thought it would be a good idea to have a module parameter that simply disables SMMU, so we were considering a fix. Best regards, Shuuichirou. > -----Original Message----- > From: Robin Murphy <robin.murphy@arm.com> > Sent: Wednesday, August 3, 2022 6:26 PM > To: Ishii, Shuuichirou/石井 周一郎 <ishii.shuuichir@fujitsu.com>; > will@kernel.org; joro@8bytes.org; thunder.leizhen@huawei.com; jgg@ziepe.ca; > tglx@linutronix.de; chenxiang66@hisilicon.com; christophe.jaillet@wanadoo.fr; > john.garry@huawei.com; baolu.lu@linux.intel.com; > linux-arm-kernel@lists.infradead.org; iommu@lists.linux.dev; > linux-kernel@vger.kernel.org > Subject: Re: [PATCH] iommu/arm-smmu-v3: fixed check process for > disable_bypass module parameter > > On 2022-08-03 00:42, Shuuichirou Ishii wrote: > > The current process does not enable the bypass setting regardless of > > the value of the disable_bypass module parameter when ACPI is enabled, > > so the value of the disable_bypass module parameter has been corrected > > so that it is handled correctly. > > > > Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@fujitsu.com> > > --- > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > index 88817a3376ef..256d7b2a83a7 100644 > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > @@ -3396,7 +3396,7 @@ static int arm_smmu_device_reset(struct > arm_smmu_device *smmu, bool bypass) > > enables &= ~(CR0_EVTQEN | CR0_PRIQEN); > > > > /* Enable the SMMU interface, or ensure bypass */ > > - if (!bypass || disable_bypass) { > > + if (!bypass && disable_bypass) { > > This change looks obviously wrong - if bypass is false here then we definitely > want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be > possible to get here with bypass==true under ACPI, since > arm_smmu_device_acpi_probe() cannot fail :/ > Robin. > > > enables |= CR0_SMMUEN; > > } else { > > ret = arm_smmu_update_gbpa(smmu, 0, GBPA_ABORT);
On 2022-08-03 13:45, ishii.shuuichir@fujitsu.com wrote: > Hi, Robin, > Thank you for your comments. > >>> /* Enable the SMMU interface, or ensure bypass */ >>> - if (!bypass || disable_bypass) { >>> + if (!bypass && disable_bypass) { >> >> This change looks obviously wrong - if bypass is false here then we definitely >> want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be >> possible to get here with bypass==true under ACPI, since >> arm_smmu_device_acpi_probe() cannot fail :/ > > Sorry, my understanding of the meaning of the disable_bypass module parameter > and the process of setting GBPA_ABORT was insufficient. > > I misunderstood that the disable_bypass module parameter is used to simply > bypass (disable) SMMU (SMMU_CR0.SMMUEN == 0 and SMMU_GBPA.ABORT == 0). > Forget about the fixes in this patch. > > Although our understanding was lacking, > we thought it would be a good idea to have a module parameter that simply disables SMMU, > so we were considering a fix. Right, disable_bypass is a security/robustness feature for when the driver *is* in use. If for some reason you want to disable the SMMU drivers completely, they are regular driver model drivers, so just don't load the module in the first place (or use initcall_blacklist if it's built-in). Thanks, Robin. > > Best regards, > Shuuichirou. > >> -----Original Message----- >> From: Robin Murphy <robin.murphy@arm.com> >> Sent: Wednesday, August 3, 2022 6:26 PM >> To: Ishii, Shuuichirou/石井 周一郎 <ishii.shuuichir@fujitsu.com>; >> will@kernel.org; joro@8bytes.org; thunder.leizhen@huawei.com; jgg@ziepe.ca; >> tglx@linutronix.de; chenxiang66@hisilicon.com; christophe.jaillet@wanadoo.fr; >> john.garry@huawei.com; baolu.lu@linux.intel.com; >> linux-arm-kernel@lists.infradead.org; iommu@lists.linux.dev; >> linux-kernel@vger.kernel.org >> Subject: Re: [PATCH] iommu/arm-smmu-v3: fixed check process for >> disable_bypass module parameter >> >> On 2022-08-03 00:42, Shuuichirou Ishii wrote: >>> The current process does not enable the bypass setting regardless of >>> the value of the disable_bypass module parameter when ACPI is enabled, >>> so the value of the disable_bypass module parameter has been corrected >>> so that it is handled correctly. >>> >>> Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@fujitsu.com> >>> --- >>> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >>> b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >>> index 88817a3376ef..256d7b2a83a7 100644 >>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >>> @@ -3396,7 +3396,7 @@ static int arm_smmu_device_reset(struct >> arm_smmu_device *smmu, bool bypass) >>> enables &= ~(CR0_EVTQEN | CR0_PRIQEN); >>> >>> /* Enable the SMMU interface, or ensure bypass */ >>> - if (!bypass || disable_bypass) { >>> + if (!bypass && disable_bypass) { >> >> This change looks obviously wrong - if bypass is false here then we definitely >> want to enable the SMMU, so disable_bypass is irrelevant. It shouldn't even be >> possible to get here with bypass==true under ACPI, since >> arm_smmu_device_acpi_probe() cannot fail :/ >> Robin. >> >>> enables |= CR0_SMMUEN; >>> } else { >>> ret = arm_smmu_update_gbpa(smmu, 0, GBPA_ABORT);
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c index 88817a3376ef..256d7b2a83a7 100644 --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c @@ -3396,7 +3396,7 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass) enables &= ~(CR0_EVTQEN | CR0_PRIQEN); /* Enable the SMMU interface, or ensure bypass */ - if (!bypass || disable_bypass) { + if (!bypass && disable_bypass) { enables |= CR0_SMMUEN; } else { ret = arm_smmu_update_gbpa(smmu, 0, GBPA_ABORT);
The current process does not enable the bypass setting regardless of the value of the disable_bypass module parameter when ACPI is enabled, so the value of the disable_bypass module parameter has been corrected so that it is handled correctly. Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@fujitsu.com> --- drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)