Re: [PATCH] iommu/vt-d: avoid unnecessory panic if iommu init fail in tboot

[Lu Baolu]

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@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >   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