Re: [Qemu-devel] [PATCH 1/2] pcie: Add a simple PCIe ACS (Access Control Services) helper function

[Knut Omang]

On Wed, 2019-01-23 at 12:32 -0700, Alex Williamson wrote:
> On Wed, 23 Jan 2019 20:14:07 +0100
> Knut Omang <address@hidden> wrote:
> 
> > On Wed, 2019-01-23 at 12:04 -0700, Alex Williamson wrote:
> > > On Wed, 23 Jan 2019 19:27:59 +0100
> > > Knut Omang <address@hidden> wrote:
> > >   
> > > > Add a helper function to add PCIe capability for Access Control 
> > > > Services (ACS)
> > > > ACS support in the associated root port is a prerequisite to be able to 
> > > > do useful
> > > > passthrough with VFIO without Alex Williamson's pcie_acs_override 
> > > > kernel patch.  
> > > 
> > > Define "useful".    
> > 
> > Hmm - just that without the patches, the root port itself 
> > also gets assigned to the same group, which seemed problematic to me
> > (without any further testing than just binding/unbinding to VFIO)
> 
> vfio-pci binding rules only apply to endpoints.  A root port lacking
> ACS will include all devices downstream of it in the IOMMU group, and
> potentially sibling functions, and devices downstream of those, but it
> doesn't absolutely preclude L2 assignment, or L1 userspace usage,
> which is already widely used.  It simply means that all the endpoints
> within that group need to be bound to vfio-pci and can only have a
> single owner.  Thanks,

I see, that makes sense - I'll moderate my language!

Thanks,
Knut
> 
> Alex
> 
> > > We can certainly still assign single function PFs to
> > > an L2 guest, or multi-function so long as all the functions are
> > > assigned.  I won't deny that it's problematic, but it's a virtual
> > > topology that can be adjusted, so I think this is overstating things a
> > > bit.
> > >   
> > > > Signed-off-by: Knut Omang <address@hidden>
> > > > ---
> > > >  hw/pci/pcie.c              | 14 ++++++++++++++
> > > >  include/hw/pci/pcie.h      |  1 +
> > > >  include/hw/pci/pcie_regs.h |  4 ++++
> > > >  3 files changed, 19 insertions(+)
> > > > 
> > > > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > > > index 230478f..18feff5 100644
> > > > --- a/hw/pci/pcie.c
> > > > +++ b/hw/pci/pcie.c
> > > > @@ -906,3 +906,17 @@ void pcie_ats_init(PCIDevice *dev, uint16_t offset)
> > > >  
> > > >      pci_set_word(dev->wmask + dev->exp.ats_cap + PCI_ATS_CTRL, 0x800f);
> > > >  }
> > > > +
> > > > +/* Add an ACS (Access Control Services) capability */
> > > > +void pcie_acs_init(PCIDevice *dev, uint16_t offset, uint8_t 
> > > > egress_ctrl_vec_sz)
> > > > +{
> > > > +    int ectrl_words = (egress_ctrl_vec_sz + 31) & ~31;
> > > > +    pcie_add_capability(dev, PCI_EXT_CAP_ID_ACS, PCI_ACS_VER,
> > > > +                        offset, PCI_ACS_SIZEOF + ectrl_words);  
> > > 
> > > The egress control vector is only valid if the egress control
> > > capability is enabled, which is not set below, so this just seems to
> > > waste config space and introduces a meaningless function arg.
> > >   
> > > > +    pci_set_word(dev->config + offset + PCI_ACS_CAP,
> > > > +                 PCI_ACS_SV | PCI_ACS_TB | PCI_ACS_RR | PCI_ACS_CR |
> PCI_ACS_UF);  
> > > 
> > > Some of these bits are only valid for downstream ports, it would
> > > violate the spec to set them on and endpoint.
> > >   
> > > > +    pci_set_word(dev->config + offset + PCI_ACS_CTRL,
> > > > +                 PCI_ACS_SV | PCI_ACS_TB | PCI_ACS_RR | PCI_ACS_CR |
> PCI_ACS_UF);  
> > > 
> > > The default values of the control register bits is zero, so we
> > > shouldn't be setting it here and we should have a reset hook to clear
> > > it.
> > >   
> > > > +    /* Make CTRL register writable */
> > > > +    memset(dev->wmask + offset + PCI_ACS_CTRL, 0xff, 2);
> > > > +}
> > > > diff --git a/include/hw/pci/pcie.h b/include/hw/pci/pcie.h
> > > > index 5b82a0d..c2da148 100644
> > > > --- a/include/hw/pci/pcie.h
> > > > +++ b/include/hw/pci/pcie.h
> > > > @@ -129,6 +129,7 @@ void pcie_add_capability(PCIDevice *dev,
> > > >  void pcie_sync_bridge_lnk(PCIDevice *dev);
> > > >  
> > > >  void pcie_ari_init(PCIDevice *dev, uint16_t offset, uint16_t nextfn);
> > > > +void pcie_acs_init(PCIDevice *dev, uint16_t offset, uint8_t 
> > > > egress_ctrl_vec_sz);
> > > >  void pcie_dev_ser_num_init(PCIDevice *dev, uint16_t offset, uint64_t 
> > > > ser_num);
> > > >  void pcie_ats_init(PCIDevice *dev, uint16_t offset);
> > > >  
> > > > diff --git a/include/hw/pci/pcie_regs.h b/include/hw/pci/pcie_regs.h
> > > > index ad4e780..5e7409c 100644
> > > > --- a/include/hw/pci/pcie_regs.h
> > > > +++ b/include/hw/pci/pcie_regs.h
> > > > @@ -175,4 +175,8 @@ typedef enum PCIExpLinkWidth {
> > > >                                           PCI_ERR_COR_INTERNAL |        
> > > >  \
> > > >                                           PCI_ERR_COR_HL_OVERFLOW)
> > > >  
> > > > +/* ACS */
> > > > +#define PCI_ACS_VER                    0x2
> > > > +#define PCI_ACS_SIZEOF                  8
> > > > +
> > > >  #endif /* QEMU_PCIE_REGS_H */  
> > >   
> > 
>