Re: [PATCH v6 2/3] xen/arm: Enable the existing x86 virtual PCI support for ARM.

[Bertrand Marquis <Bertrand.Marquis@arm.com>]

Hi Luca,

> On 15 Oct 2021, at 11:13, Luca Fancellu <Luca.Fancellu@arm.com> wrote:
> 
> 
> 
>> On 15 Oct 2021, at 10:52, Bertrand Marquis <Bertrand.Marquis@arm.com> wrote:
>> 
>> Hi Roger,
>> 
>>> On 15 Oct 2021, at 09:32, Roger Pau Monné <roger.pau@citrix.com> wrote:
>>> 
>>> On Thu, Oct 14, 2021 at 03:49:50PM +0100, Bertrand Marquis wrote:
>>>> From: Rahul Singh <rahul.singh@arm.com>
>>>> 
>>>> The existing VPCI support available for X86 is adapted for Arm.
>>>> When the device is added to XEN via the hyper call
>>>> “PHYSDEVOP_pci_device_add”, VPCI handler for the config space
>>>> access is added to the Xen to emulate the PCI devices config space.
>>>> 
>>>> A MMIO trap handler for the PCI ECAM space is registered in XEN
>>>> so that when guest is trying to access the PCI config space,XEN
>>>> will trap the access and emulate read/write using the VPCI and
>>>> not the real PCI hardware.
>>>> 
>>>> For Dom0less systems scan_pci_devices() would be used to discover the
>>>> PCI device in XEN and VPCI handler will be added during XEN boots.
>>>> 
>>>> This patch is also doing some small fixes to fix compilation errors on
>>>> arm32 of vpci:
>>>> - add a cast to unsigned long in print in header.c
>>>> - add a cast to uint64_t in vpci_ecam_mmio_write
>>>> 
>>>> Signed-off-by: Rahul Singh <rahul.singh@arm.com>
>>>> Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
>>>> ---
>>>> Changes in v6:
>>>> - Use new vpci_ecam_ helpers for PCI access
>>>> - Do not set XEN_DOMCTL_CDF_vpci for dom0 for now (will be done in a
>>>> future patch once everything is ready)
>>> 
>>> Isn't the series missing a revert of XEN_DOMCTL_CDF_vpci? I think
>>> that's what we agreed would be the way forward.
>> 
>> A separate reverse patch for that has already been merged:
>> https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=9516d01ac3015f522528ed6dafb3f584eaa7ed2c
>> 
>>> 
>>>> - rename REGISTER_OFFSET to ECAM_REG_OFFSET and move it to pci.h
>>>> - remove not needed local variables in vpci_mmio_write, the one in read
>>>> has been kept to ensure proper compilation on arm32
>>>> - move call to vpci_add_handlers before iommu init to simplify exit path
>>>> - move call to pci_cleanup_msi in the out section of pci_add_device if
>>>> pdev is not NULL and on error
>>>> - initialize pdev to NULL to handle properly exit path call of
>>>> pci_cleanup_msi
>>>> - keep has_vpci to return false for now as CFG_vpci has been removed.
>>>> Added a comment on top of the definition.
>>>> - fix compilation errors on arm32 (print in header.c, cast missing in
>>>> mmio_write.
>>>> - local variable was kept in vpci_mmio_read on arm to prevent a cast
>>>> error in arm32.
>>>> Change in v5:
>>>> - Add pci_cleanup_msi(pdev) incleanup part.
>>>> - Added Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
>>>> Change in v4:
>>>> - Move addition of XEN_DOMCTL_CDF_vpci flag to separate patch
>>>> Change in v3:
>>>> - Use is_pci_passthrough_enabled() in place of pci_passthrough_enabled variable
>>>> - Reject XEN_DOMCTL_CDF_vpci for x86 in arch_sanitise_domain_config()
>>>> - Remove IS_ENABLED(CONFIG_HAS_VPCI) from has_vpci()
>>>> Change in v2:
>>>> - Add new XEN_DOMCTL_CDF_vpci flag
>>>> - modify has_vpci() to include XEN_DOMCTL_CDF_vpci
>>>> - enable vpci support when pci-passthough option is enabled.
>>>> ---
>>>> ---
>>>> xen/arch/arm/Makefile         |  1 +
>>>> xen/arch/arm/domain.c         |  4 ++
>>>> xen/arch/arm/vpci.c           | 74 +++++++++++++++++++++++++++++++++++
>>>> xen/arch/arm/vpci.h           | 36 +++++++++++++++++
>>>> xen/drivers/passthrough/pci.c | 18 ++++++++-
>>>> xen/drivers/vpci/header.c     |  3 +-
>>>> xen/drivers/vpci/vpci.c       |  2 +-
>>>> xen/include/asm-arm/domain.h  |  1 +
>>>> xen/include/asm-x86/pci.h     |  2 -
>>>> xen/include/public/arch-arm.h |  7 ++++
>>>> xen/include/xen/pci.h         |  3 ++
>>>> 11 files changed, 146 insertions(+), 5 deletions(-)
>>>> create mode 100644 xen/arch/arm/vpci.c
>>>> create mode 100644 xen/arch/arm/vpci.h
>>>> 
>>>> diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
>>>> index 64518848b2..07f634508e 100644
>>>> --- a/xen/arch/arm/Makefile
>>>> +++ b/xen/arch/arm/Makefile
>>>> @@ -7,6 +7,7 @@ ifneq ($(CONFIG_NO_PLAT),y)
>>>> obj-y += platforms/
>>>> endif
>>>> obj-$(CONFIG_TEE) += tee/
>>>> +obj-$(CONFIG_HAS_VPCI) += vpci.o
>>>> 
>>>> obj-$(CONFIG_HAS_ALTERNATIVE) += alternative.o
>>>> obj-y += bootfdt.init.o
>>>> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
>>>> index eef0661beb..96e1b23550 100644
>>>> --- a/xen/arch/arm/domain.c
>>>> +++ b/xen/arch/arm/domain.c
>>>> @@ -39,6 +39,7 @@
>>>> #include <asm/vgic.h>
>>>> #include <asm/vtimer.h>
>>>> 
>>>> +#include "vpci.h"
>>>> #include "vuart.h"
>>>> 
>>>> DEFINE_PER_CPU(struct vcpu *, curr_vcpu);
>>>> @@ -773,6 +774,9 @@ int arch_domain_create(struct domain *d,
>>>>   if ( is_hardware_domain(d) && (rc = domain_vuart_init(d)) )
>>>>       goto fail;
>>>> 
>>>> +    if ( (rc = domain_vpci_init(d)) != 0 )
>>>> +        goto fail;
>>>> +
>>>>   return 0;
>>>> 
>>>> fail:
>>>> diff --git a/xen/arch/arm/vpci.c b/xen/arch/arm/vpci.c
>>>> new file mode 100644
>>>> index 0000000000..7c3552b65d
>>>> --- /dev/null
>>>> +++ b/xen/arch/arm/vpci.c
>>>> @@ -0,0 +1,74 @@
>>>> +/*
>>>> + * xen/arch/arm/vpci.c
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License as published by
>>>> + * the Free Software Foundation; either version 2 of the License, or
>>>> + * (at your option) any later version.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful,
>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>> + * GNU General Public License for more details.
>>>> + */
>>>> +#include <xen/sched.h>
>>>> +#include <xen/vpci.h>
>>>> +
>>>> +#include <asm/mmio.h>
>>>> +
>>>> +static int vpci_mmio_read(struct vcpu *v, mmio_info_t *info,
>>>> +                          register_t *r, void *p)
>>>> +{
>>>> +    pci_sbdf_t sbdf;
>>>> +    /* data is needed to prevent a pointer cast on 32bit */
>>>> +    unsigned long data = ~0ul;
>>>> +    int ret;
>>>> +
>>>> +    /* We ignore segment part and always handle segment 0 */
>>>> +    sbdf.sbdf = ECAM_BDF(info->gpa);
>>>> +
>>>> +    ret = vpci_ecam_mmio_read(sbdf, ECAM_REG_OFFSET(info->gpa),
>>>> +                              1U << info->dabt.size, &data);
>>>> +
>>>> +    *r = data;
>>>> +
>>>> +    return ret;
>>>> +}
>>>> +
>>>> +static int vpci_mmio_write(struct vcpu *v, mmio_info_t *info,
>>>> +                           register_t r, void *p)
>>>> +{
>>>> +    pci_sbdf_t sbdf;
>>>> +
>>>> +    /* We ignore segment part and always handle segment 0 */
>>>> +    sbdf.sbdf = ECAM_BDF(info->gpa);
>>>> +
>>>> +    return vpci_ecam_mmio_write(sbdf, ECAM_REG_OFFSET(info->gpa),
>>>> +                                1U << info->dabt.size, r);
>>>> +}
>>> 
>>> I'm not sure returning an error value here is helpful, as I'm not sure
>>> how native Arm behaves and how this error is propagated into the
>>> guest. FWIWreturning ~0 or dropping writes is what we do in x86 when
>>> vPCI is not capable of handling the access.
>> 
>> Mmio handlers can take a return code on arm if something did not work
>> so I think this is the right way to do it on arm.
>> Now has agreed with Jan, we will change the return type of 
>> vpci_ecam_write (also renamed) to be a boolean.
>> 
>>> 
>>>> +
>>>> +static const struct mmio_handler_ops vpci_mmio_handler = {
>>>> +    .read  = vpci_mmio_read,
>>>> +    .write = vpci_mmio_write,
>>>> +};
>>>> +
>>>> +int domain_vpci_init(struct domain *d)
>>>> +{
>>>> +    if ( !has_vpci(d) )
>>>> +        return 0;
>>>> +
>>>> +    register_mmio_handler(d, &vpci_mmio_handler,
>>>> +                          GUEST_VPCI_ECAM_BASE, GUEST_VPCI_ECAM_SIZE, NULL);
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +/*
>>>> + * Local variables:
>>>> + * mode: C
>>>> + * c-file-style: "BSD"
>>>> + * c-basic-offset: 4
>>>> + * indent-tabs-mode: nil
>>>> + * End:
>>>> + */
>>>> +
>>>> diff --git a/xen/arch/arm/vpci.h b/xen/arch/arm/vpci.h
>>>> new file mode 100644
>>>> index 0000000000..d8a7b0e3e8
>>>> --- /dev/null
>>>> +++ b/xen/arch/arm/vpci.h
>>>> @@ -0,0 +1,36 @@
>>>> +/*
>>>> + * xen/arch/arm/vpci.h
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License as published by
>>>> + * the Free Software Foundation; either version 2 of the License, or
>>>> + * (at your option) any later version.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful,
>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>> + * GNU General Public License for more details.
>>>> + */
>>>> +
>>>> +#ifndef __ARCH_ARM_VPCI_H__
>>>> +#define __ARCH_ARM_VPCI_H__
>>>> +
>>>> +#ifdef CONFIG_HAS_VPCI
>>>> +int domain_vpci_init(struct domain *d);
>>>> +#else
>>>> +static inline int domain_vpci_init(struct domain *d)
>>>> +{
>>>> +    return 0;
>>>> +}
>>>> +#endif
>>>> +
>>>> +#endif /* __ARCH_ARM_VPCI_H__ */
>>>> +
>>>> +/*
>>>> + * Local variables:
>>>> + * mode: C
>>>> + * c-file-style: "BSD"
>>>> + * c-basic-offset: 4
>>>> + * indent-tabs-mode: nil
>>>> + * End:
>>>> + */
>>>> diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
>>>> index 3aa8c3175f..8cc529ecec 100644
>>>> --- a/xen/drivers/passthrough/pci.c
>>>> +++ b/xen/drivers/passthrough/pci.c
>>>> @@ -658,7 +658,7 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
>>>>                  const struct pci_dev_info *info, nodeid_t node)
>>>> {
>>>>   struct pci_seg *pseg;
>>>> -    struct pci_dev *pdev;
>>>> +    struct pci_dev *pdev = NULL;
>>>>   unsigned int slot = PCI_SLOT(devfn), func = PCI_FUNC(devfn);
>>>>   const char *pdev_type;
>>>>   int ret;
>>>> @@ -752,6 +752,19 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
>>>> 
>>>>   check_pdev(pdev);
>>>> 
>>>> +#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.
>>>> +     */
>>>> +    ret = vpci_add_handlers(pdev);
>>>> +    if ( ret )
>>>> +    {
>>>> +        printk(XENLOG_ERR "Setup of vPCI failed: %d\n", ret);
>>>> +        goto out;
>>>> +    }
>>>> +#endif
>>> 
>>> I think vpci_add_handlers should be called after checking that
>>> pdev->domain is != NULL, so I would move this chunk a bit below.
>> 
>> On arm this would prevent the dom0less use case or to have the PCI
>> bus enumerated from an other domain.
>> @oleksandr: can you comment on this one, you might have a better
>> answer than me on this ?
> 
> For my understanding, as also Jan pointed out, this should be put inside the
> If ( !pdev->domain ) because also as the comment suggests, this operation
> should be performed only when there is a Dom0 and when we are using
> a dom0less setup the pdev->domain should be NULL if I’m not wrong.
> @oleksandr maybe can confirm

You are right.
I will fix that and move that into an if.

Regards
Bertrand

> 
>> 
>>> 
>>>> +
>>>>   ret = 0;
>>>>   if ( !pdev->domain )
>>>>   {
>>>> @@ -784,6 +797,9 @@ out:
>>>>                  &PCI_SBDF(seg, bus, slot, func));
>>>>       }
>>>>   }
>>>> +    else if ( pdev )
>>>> +        pci_cleanup_msi(pdev);
>>> 
>>> I'm slightly lost at why you add this chunk, is this strictly related
>>> to the patch?
>> 
>> This was discussed a lot in previous version of the patch and
>> requested by Stefano. The idea here is that as soon as handlers
>> are added some bits might be modified in the PCI config space
>> leading possibly to msi interrupts. So it is safer to cleanup on the
>> error path. For references please see discussion on v4 and v5 where
>> this was actually added (to much references as the discussion was
>> long so here [1] and [2] are the patchwork thread).
>> 
>> [1] https://patchwork.kernel.org/project/xen-devel/patch/9bdca2cda5d2e83f94dc2423e55714273539760a.1633540842.git.rahul.singh@arm.com/
>> [2] https://patchwork.kernel.org/project/xen-devel/patch/f093de681c2560a7196895bcd666ef8840885c1d.1633340795.git.rahul.singh@arm.com/
>> 
>> Regards
>> Bertrand