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Message-ID: <f551eecc-33fa-4729-b004-64a532493705@quicinc.com>
Date: Thu, 18 Jul 2024 15:43:18 +0530
From: Pavan Kondeti <quic_pkondeti@...cinc.com>
To: Will Deacon <will@...nel.org>, Vidya Sagar <vidyas@...dia.com>
CC: Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J. Wysocki"
	<rafael@...nel.org>,
        Krzysztof WilczyƄski <kw@...ux.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        Manikanta Maddireddy
	<mmaddireddy@...dia.com>,
        Shanker Donthineni <sdonthineni@...dia.com>,
        Krishna Thota <kthota@...dia.com>, Joerg Roedel <joro@...tes.org>
Subject: Re: [Query] ACS enablement in the DT based boot flow

Hi Vidya/Will,

On Sun, Apr 28, 2024 at 08:23:18AM +0100, Will Deacon wrote:
> On Wed, Apr 10, 2024 at 02:28:40PM -0500, Bjorn Helgaas wrote:
> > [+cc Will, Joerg]
> > 
> > On Mon, Apr 01, 2024 at 10:40:15AM +0000, Vidya Sagar wrote:
> > > Hi folks,
> > > ACS (Access Control Services) is configured for a PCI device through
> > > pci_enable_acs().  The first thing pci_enable_acs() checks for is
> > > whether the global flag 'pci_acs_enable' is set or not.  The global
> > > flag 'pci_acs_enable' is set by the function pci_request_acs().
> > > 
> > > pci_enable_acs() function is called whenever a new PCI device is
> > > added to the system
> > > 
> > >  pci_enable_acs+0x4c/0x2a4
> > >  pci_acs_init+0x38/0x60
> > >  pci_device_add+0x1a0/0x670
> > >  pci_scan_single_device+0xc4/0x100
> > >  pci_scan_slot+0x6c/0x1e0
> > >  pci_scan_child_bus_extend+0x48/0x2e0
> > >  pci_scan_root_bus_bridge+0x64/0xf0
> > >  pci_host_probe+0x18/0xd0
> > > 
> > > In the case of a system that boots using device-tree blob,
> > > pci_request_acs() is called when the device driver binds with the
> > > respective device
> > > 
> > > of_iommu_configure+0xf4/0x230
> > > of_dma_configure_id+0x110/0x340
> > > pci_dma_configure+0x54/0x120
> > > really_probe+0x80/0x3e0
> > > __driver_probe_device+0x88/0x1c0
> > > driver_probe_device+0x3c/0x140
> > > __device_attach_driver+0xe8/0x1e0
> > > bus_for_each_drv+0x78/0xf0
> > > __device_attach+0x104/0x1e0
> > > device_attach+0x14/0x30
> > > pci_bus_add_device+0x50/0xd0
> > > pci_bus_add_devices+0x38/0x90
> > > pci_host_probe+0x40/0xd0
> > > 
> > > Since the device addition always happens first followed by the
> > > driver binding, this flow effectively makes sure that ACS never gets
> > > enabled.
> > > 
> > > Ideally, I would expect the pci_request_acs() get called (probably
> > > by the OF framework itself) before calling pci_enable_acs().
> > > 
> > > This happens in the ACPI flow where pci_request_acs() is called
> > > during IORT node initialization (i.e. iort_init_platform_devices()
> > > function).
> > > 
> > > Is this understanding correct? If yes, would it make sense to call
> > > pci_request_acs() during OF initialization (similar to IORT
> > > initialization in ACPI flow)?
> > 
> > Your understanding looks correct to me.  My call graph notes, FWIW:
> > 
> >   mem_init
> >     pci_iommu_alloc                   # x86 only
> >       amd_iommu_detect                # init_state = IOMMU_START_STATE
> >         iommu_go_to_state(IOMMU_IVRS_DETECTED)
> >           state_next
> >             switch (init_state)
> >             case IOMMU_START_STATE:
> >               detect_ivrs
> >                 pci_request_acs
> >                   pci_acs_enable = 1  # <--
> >       detect_intel_iommu
> >         pci_request_acs
> >           pci_acs_enable = 1          # <--
> > 
> >   pci_scan_single_device              # PCI enumeration
> >     ...
> >       pci_init_capabilities
> >         pci_acs_init
> >           pci_enable_acs
> >             if (pci_acs_enable)       # <--
> >               pci_std_enable_acs
> > 
> >   __driver_probe_device
> >     really_probe
> >       pci_dma_configure               # pci_bus_type.dma_configure
> >         if (OF)
> >           of_dma_configure
> >             of_dma_configure_id
> >               of_iommu_configure
> >                 pci_request_acs       # <-- 6bf6c24720d3
> >                 iommu_probe_device
> >         else if (ACPI)
> >           acpi_dma_configure
> >             acpi_dma_configure_id
> >               acpi_iommu_configure_id
> >                 iommu_probe_device
> > 
> > The pci_request_acs() in of_iommu_configure(), which happens too late
> > to affect pci_enable_acs(), was added by 6bf6c24720d3 ("iommu/of:
> > Request ACS from the PCI core when configuring IOMMU linkage"), so I
> > cc'd Will and Joerg.  I don't know if that *used* to work and got
> > broken somehow, or if it never worked as intended.
> 
> I don't have any way to test this, but I'm supportive of having the same
> flow for DT and ACPI-based flows. Vidya, are you able to cook a patch?
> 

I ran into a similar observation while testing a PCI device assignment
to a VM. In my configuration, the virtio-iommu is enumerated over the
PCI transport. So, I am thinking we can't hook pci_request_acs() to an
IOMMU driver. Does the below patch makes sense?

The patch is tested with a VM and I could see ACS getting enabled and
separate IOMMU groups are created for the devices attached under
PCIe root port(s).

The RC/devices with ACS quirks are not suffering from this problem as we 
short circuit ACS capability detection checking in
pci_acs_enabled()->pci_dev_specific_acs_enabled() . May be this is one
of the reason why this was not reported/observed by some platforms with
DT.

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index b908fe1ae951..0eeb7abfbcfa 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -123,6 +123,13 @@ bool pci_host_of_has_msi_map(struct device *dev)
 	return false;
 }
 
+bool pci_host_of_has_iommu_map(struct device *dev)
+{
+	if (dev && dev->of_node)
+		return of_get_property(dev->of_node, "iommu-map", NULL);
+	return false;
+}
+
 static inline int __of_pci_pci_compare(struct device_node *node,
 				       unsigned int data)
 {
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4c367f13acdc..ea6fcdaf63e2 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -889,6 +889,7 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+bool pci_host_of_has_iommu(struct device *dev);
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -951,6 +952,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	    !pci_host_of_has_msi_map(parent))
 		bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
 
+	if (pci_host_of_has_iommu_map(parent))
+		pci_request_acs();
+
 	if (!parent)
 		set_dev_node(bus->bridge, pcibus_to_node(bus));
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index cafc5ab1cbcb..7eceed71236a 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2571,6 +2571,7 @@ struct device_node;
 struct irq_domain;
 struct irq_domain *pci_host_bridge_of_msi_domain(struct pci_bus *bus);
 bool pci_host_of_has_msi_map(struct device *dev);
+bool pci_host_of_has_iommu_map(struct device *dev);
 
 /* Arch may override this (weak) */
 struct device_node *pcibios_get_phb_of_node(struct pci_bus *bus);
@@ -2579,6 +2580,7 @@ struct device_node *pcibios_get_phb_of_node(struct pci_bus *bus);
 static inline struct irq_domain *
 pci_host_bridge_of_msi_domain(struct pci_bus *bus) { return NULL; }
 static inline bool pci_host_of_has_msi_map(struct device *dev) { return false; }
+static inline bool pci_host_of_has_iommu_map(struct device *dev) { return false; }
 #endif  /* CONFIG_OF */
 
 static inline struct device_node *

Thanks,
Pavan



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