> -----Original Message-----
> From: Lu Baolu <[email protected]>
> Sent: Wednesday, January 20, 2021 10:35 AM
> To: Zhang, Tina <[email protected]>
> Cc: [email protected]; [email protected]; Joerg
> Roedel <[email protected]>; Mehta, Sohil <[email protected]>; Jacob
> Pan <[email protected]>; Sun, Yi <[email protected]>
> Subject: Re: [PATCH] iommu/vt-d: debugfs: Check irq_remapping_cap before
> PI info dump
>
> On 1/20/21 2:25 AM, Tina Zhang wrote:
> > irq_remapping_cap() was introduced to detect whether irq remapping
> > supports new features, such as VT-d Posted-Interrupts", according to
> > commit 959c870f7305 ("iommu, x86: Provide irq_remapping_cap()
> interface").
> >
> > The VT-d Posted-Interrupts support can be disabled by the command line
> > parameter "intremap=nopost".
> >
> > So, it's better to use irq_remapping_cap() to check if the VT-d
> > Posted-Interrupts is enabled before any Posted Interrupt Descriptor
> > info dump.
> >
> > Cc: Lu Baolu <[email protected]>
> > Cc: Joerg Roedel <[email protected]>
> > Cc: Sohil Mehta <[email protected]>
> > Cc: Jacob Pan <[email protected]>
> > Reported-by: Yi Sun <[email protected]>
> > Signed-off-by: Tina Zhang <[email protected]>
> > ---
> > drivers/iommu/intel/debugfs.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/intel/debugfs.c
> > b/drivers/iommu/intel/debugfs.c index efea7f02abd9..87a4a76866f4
> > 100644
> > --- a/drivers/iommu/intel/debugfs.c
> > +++ b/drivers/iommu/intel/debugfs.c
> > @@ -516,7 +516,8 @@ static int ir_translation_struct_show(struct seq_file
> *m, void *unused)
> > seq_puts(m, "****\n\n");
> >
> > for_each_active_iommu(iommu, drhd) {
> > - if (!cap_pi_support(iommu->cap))
> > + if (!irq_remapping_cap(IRQ_POSTING_CAP) ||
> > + !cap_pi_support(iommu->cap))
>
> With irq_remapping_cap(IRQ_POSTING_CAP), do you still need
> cap_pi_support(iommu->cap)?
I guess yes. The "iommu->cap" value comes from the iommu reg. Current code
seems to use cap_pi_suport() to check if the iommu hardware supports PI
capability, meanwhile using irq_remapping_cap() to see if the vt-d PI support
is enabled by user.
So, the problem here is if a user explicitly disables the vt-d PI support by
"intremap=nopost", it would be very confused that the PI descriptor related
info can still get dump.
Thanks,
Tina
>
> > continue;
> >
> > seq_printf(m, "Posted Interrupt supported on
> IOMMU: %s\n",
> >
>
> Best regards,
> baolu
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