Re: [PATCH v2 1/1] xen/pci: Install vpci handlers on x86 and fix exit path

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Oct 20, 2021 at 07:57:15AM +0000, Bertrand Marquis wrote:
> Hi Roger,
> 
> > On 20 Oct 2021, at 08:49, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> > 
> > On Tue, Oct 19, 2021 at 05:08:28PM +0100, Bertrand Marquis wrote:
> >> Xen might not be able to discover at boot time all devices or some devices
> >> might appear after specific actions from dom0.
> >> In this case dom0 can use the PHYSDEVOP_pci_device_add to signal some
> >> PCI devices to Xen.
> >> As those devices where not known from Xen before, the vpci handlers must
> >> be properly installed during pci_device_add for x86 PVH Dom0, in the
> >> same way as what is done currently on arm (where Xen does not detect PCI
> >> devices but relies on Dom0 to declare them all the time).
> >> 
> >> So this patch is removing the ifdef protecting the call to
> >> vpci_add_handlers and the comment which was arm specific.
> >> 
> >> vpci_add_handlers is called on during pci_device_add which can be called
> >> at runtime through hypercall physdev_op.
> >> Remove __hwdom_init as the call is not limited anymore to hardware
> >> domain init and fix linker script to only keep vpci_array in rodata
> >> section.
> >> 
> >> Add missing vpci handlers cleanup during pci_device_remove and in case
> >> of error with iommu during pci_device_add.
> >> 
> >> Add empty static inline for vpci_remove_device when CONFIG_VPCI is not
> >> defined.
> >> 
> >> Fixes: d59168dc05 ("xen/arm: Enable the existing x86 virtual PCI support
> >> for ARM")
> >> Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
> >> Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> >> ---
> >> Changes in v2
> >> - add comment suggested by Jan on top of vpci_add_handlers call
> >> - merge the 3 patches of the serie in one patch and renamed it
> >> - fix x86 and arm linker script to only keep vpci_array in rodata and
> >> only when CONFIG_VPCI is set.
> >> ---
> >> xen/arch/arm/xen.lds.S        | 9 +--------
> >> xen/arch/x86/xen.lds.S        | 9 +--------
> >> xen/drivers/passthrough/pci.c | 8 ++++----
> >> xen/drivers/vpci/vpci.c       | 2 +-
> >> xen/include/xen/vpci.h        | 2 ++
> >> 5 files changed, 9 insertions(+), 21 deletions(-)
> >> 
> >> diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
> >> index b773f91f1c..08016948ab 100644
> >> --- a/xen/arch/arm/xen.lds.S
> >> +++ b/xen/arch/arm/xen.lds.S
> >> @@ -60,7 +60,7 @@ SECTIONS
> >>        *(.proc.info)
> >>        __proc_info_end = .;
> >> 
> >> -#if defined(CONFIG_HAS_VPCI) && defined(CONFIG_LATE_HWDOM)
> >> +#ifdef CONFIG_HAS_VPCI
> >>        . = ALIGN(POINTER_ALIGN);
> >>        __start_vpci_array = .;
> >>        *(SORT(.data.vpci.*))
> >> @@ -189,13 +189,6 @@ SECTIONS
> >>        *(.init_array)
> >>        *(SORT(.init_array.*))
> >>        __ctors_end = .;
> >> -
> >> -#if defined(CONFIG_HAS_VPCI) && !defined(CONFIG_LATE_HWDOM)
> >> -       . = ALIGN(POINTER_ALIGN);
> >> -       __start_vpci_array = .;
> >> -       *(SORT(.data.vpci.*))
> >> -       __end_vpci_array = .;
> >> -#endif
> >>   } :text
> >>   __init_end_efi = .;
> >>   . = ALIGN(STACK_SIZE);
> >> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> >> index 11b1da2154..87e344d4dd 100644
> >> --- a/xen/arch/x86/xen.lds.S
> >> +++ b/xen/arch/x86/xen.lds.S
> >> @@ -134,7 +134,7 @@ SECTIONS
> >>        *(.ex_table.pre)
> >>        __stop___pre_ex_table = .;
> >> 
> >> -#if defined(CONFIG_HAS_VPCI) && defined(CONFIG_LATE_HWDOM)
> >> +#ifdef CONFIG_HAS_VPCI
> >>        . = ALIGN(POINTER_ALIGN);
> >>        __start_vpci_array = .;
> >>        *(SORT(.data.vpci.*))
> >> @@ -247,13 +247,6 @@ SECTIONS
> >>        *(.init_array)
> >>        *(SORT(.init_array.*))
> >>        __ctors_end = .;
> >> -
> >> -#if defined(CONFIG_HAS_VPCI) && !defined(CONFIG_LATE_HWDOM)
> >> -       . = ALIGN(POINTER_ALIGN);
> >> -       __start_vpci_array = .;
> >> -       *(SORT(.data.vpci.*))
> >> -       __end_vpci_array = .;
> >> -#endif
> >>   } PHDR(text)
> >> 
> >>   . = ALIGN(SECTION_ALIGN);
> >> diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
> >> index 35e0190796..8928a1c07d 100644
> >> --- a/xen/drivers/passthrough/pci.c
> >> +++ b/xen/drivers/passthrough/pci.c
> >> @@ -756,10 +756,9 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
> >>     if ( !pdev->domain )
> >>     {
> >>         pdev->domain = hardware_domain;
> >> -#ifdef CONFIG_ARM
> >>         /*
> >> -         * On ARM PCI devices discovery will be done by Dom0. Add vpci 
> >> handler
> >> -         * when Dom0 inform XEN to add the PCI devices in XEN.
> >> +         * For devices not discovered by Xen during boot, add vPCI 
> >> handlers
> >> +         * when Dom0 first informs Xen about such devices.
> >>          */
> >>         ret = vpci_add_handlers(pdev);
> >>         if ( ret )
> >> @@ -768,10 +767,10 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
> >>             pdev->domain = NULL;
> >>             goto out;
> >>         }
> >> -#endif
> >>         ret = iommu_add_device(pdev);
> >>         if ( ret )
> >>         {
> >> +            vpci_remove_device(pdev);
> >>             pdev->domain = NULL;
> >>             goto out;
> >>         }
> >> @@ -819,6 +818,7 @@ int pci_remove_device(u16 seg, u8 bus, u8 devfn)
> >>     list_for_each_entry ( pdev, &pseg->alldevs_list, alldevs_list )
> >>         if ( pdev->bus == bus && pdev->devfn == devfn )
> >>         {
> >> +            vpci_remove_device(pdev);
> > 
> > vpci_remove_device is missing a check for has_vpci(pdev->domain), as
> > it will unconditionally access pdev->vpci otherwise, and that would be
> > wrong for domains not using vpci.
> > 
> > It might also be good to add an ASSERT(!pdev->vpci) to
> > vpci_add_handlers in order to make sure there are no duplicated calls
> > to vpci_add_handlers, but that can be done in a separate patch.
> 
> I can do both in v3 (together with the change of in the patch name).
> 
> Unless you want the ASSERT in a different patch, in this case I do not think
> I can make a new patch for that.
> 
> Can you confirm if I should or not add the ASSERT directly in the patch ?

I'm fine with having the assert added here: in wasn't necessary
previously as there was a single caller of vpci_add_handlers. Now that
there are multiple ones we should make sure no duplicated calls can
happen.

On a different note (and not something that should be solved here,
just wanted to raise attention to it) there's an existing TODO about
vpci_remove_device because it doesn't clean the 2nd stage mappings for
BARs. At some point we need to solve this, or else the removal of the
device is not complete.

Thanks, Roger.