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SubjectRe: [PATCH] iommu/vt-d: avoid unnecessory panic if iommu init fail in tboot
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Hi Zhenzhong,

On 11/9/20 10:27 AM, Zhenzhong Duan wrote:
> +intel iommu maintainers,
>
> Can anyone help review this patch? Thanks
>
> Zhenzhong
>
> On Wed, Nov 4, 2020 at 4:15 PM Zhenzhong Duan <zhenzhong.duan@gmail.com> wrote:
>>
>> "intel_iommu=off" command line is used to disable iommu and iommu is force
>> enabled in a tboot system. Meanwhile "intel_iommu=tboot_noforce,off"
>> could be used to force disable iommu in tboot for better performance.
>>
>> By default kernel should panic if iommu init fail in tboot for security
>> reason, but it's unnecessory if we use "intel_iommu=tboot_noforce,off".
>>
>> Fix it by return 0 in tboot_force_iommu() so that force_on is not set.
>>
>> Fixes: 7304e8f28bb2 ("iommu/vt-d: Correctly disable Intel IOMMU force on")
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
>> ---
>> arch/x86/kernel/tboot.c | 5 +----
>> 1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
>> index 992fb1415c0f..9fd4d162b331 100644
>> --- a/arch/x86/kernel/tboot.c
>> +++ b/arch/x86/kernel/tboot.c
>> @@ -511,12 +511,9 @@ struct acpi_table_header *tboot_get_dmar_table(struct acpi_table_header *dmar_tb
>>
>> int tboot_force_iommu(void)
>> {
>> - if (!tboot_enabled())
>> + if (!tboot_enabled() || intel_iommu_tboot_noforce)
>> return 0;
>>
>> - if (intel_iommu_tboot_noforce)
>> - return 1;

This was obviously wrong. It should return false, right?

It looks odd that intel_iommu_tboot_noforce is defined in Intel iommu
implementation, but is used here. How about moving it back to the iommu
driver?

diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
index 992fb1415c0f..420be871d9d4 100644
--- a/arch/x86/kernel/tboot.c
+++ b/arch/x86/kernel/tboot.c
@@ -514,9 +514,6 @@ int tboot_force_iommu(void)
if (!tboot_enabled())
return 0;

- if (intel_iommu_tboot_noforce)
- return 1;
-
if (no_iommu || swiotlb || dmar_disabled)
pr_warn("Forcing Intel-IOMMU to enabled\n");

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index a41f9f13cc86..ba90eb4325d0 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -179,7 +179,7 @@ static int rwbf_quirk;
* (used when kernel is launched w/ TXT)
*/
static int force_on = 0;
-int intel_iommu_tboot_noforce;
+static int intel_iommu_tboot_noforce;
static int no_platform_optin;

#define ROOT_ENTRY_NR (VTD_PAGE_SIZE/sizeof(struct root_entry))
@@ -4212,7 +4212,8 @@ int __init intel_iommu_init(void)
* Intel IOMMU is required for a TXT/tboot launch or platform
* opt in, so enforce that.
*/
- force_on = tboot_force_iommu() || platform_optin_force_iommu();
+ force_on = (!intel_iommu_tboot_noforce && tboot_force_iommu()) ||
+ platform_optin_force_iommu();

if (iommu_init_mempool()) {
if (force_on)
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index fbf5b3e7707e..d956987ed032 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -798,7 +798,6 @@ extern int iommu_calculate_agaw(struct intel_iommu
*iommu);
extern int iommu_calculate_max_sagaw(struct intel_iommu *iommu);
extern int dmar_disabled;
extern int intel_iommu_enabled;
-extern int intel_iommu_tboot_noforce;
extern int intel_iommu_gfx_mapped;
#else
static inline int iommu_calculate_agaw(struct intel_iommu *iommu)
>> -
>> if (no_iommu || swiotlb || dmar_disabled)
>> pr_warn("Forcing Intel-IOMMU to enabled\n");
>>
>> --
>> 2.25.1
>>

Best regards,
baolu

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