Re: [PATCH v16 QEMU 04/16] vfio: Add save and load functions for VFIO PCI devices

[Yan Zhao]

On Tue, May 05, 2020 at 12:37:11PM +0800, Alex Williamson wrote:
> On Tue, 5 May 2020 04:48:37 +0530
> Kirti Wankhede <address@hidden> wrote:
> 
> > On 3/26/2020 1:26 AM, Alex Williamson wrote:
> > > On Wed, 25 Mar 2020 02:39:02 +0530
> > > Kirti Wankhede <address@hidden> wrote:
> > >   
> > >> These functions save and restore PCI device specific data - config
> > >> space of PCI device.
> > >> Tested save and restore with MSI and MSIX type.
> > >>
> > >> Signed-off-by: Kirti Wankhede <address@hidden>
> > >> Reviewed-by: Neo Jia <address@hidden>
> > >> ---
> > >>   hw/vfio/pci.c                 | 163 
> > >> ++++++++++++++++++++++++++++++++++++++++++
> > >>   include/hw/vfio/vfio-common.h |   2 +
> > >>   2 files changed, 165 insertions(+)
> > >>
> > >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> > >> index 6c77c12e44b9..8deb11e87ef7 100644
> > >> --- a/hw/vfio/pci.c
> > >> +++ b/hw/vfio/pci.c
> > >> @@ -41,6 +41,7 @@
> > >>   #include "trace.h"
> > >>   #include "qapi/error.h"
> > >>   #include "migration/blocker.h"
> > >> +#include "migration/qemu-file.h"
> > >>   
> > >>   #define TYPE_VFIO_PCI "vfio-pci"
> > >>   #define PCI_VFIO(obj)    OBJECT_CHECK(VFIOPCIDevice, obj, 
> > >> TYPE_VFIO_PCI)
> > >> @@ -1632,6 +1633,50 @@ static void vfio_bars_prepare(VFIOPCIDevice *vdev)
> > >>       }
> > >>   }
> > >>   
> > >> +static int vfio_bar_validate(VFIOPCIDevice *vdev, int nr)
> > >> +{
> > >> +    PCIDevice *pdev = &vdev->pdev;
> > >> +    VFIOBAR *bar = &vdev->bars[nr];
> > >> +    uint64_t addr;
> > >> +    uint32_t addr_lo, addr_hi = 0;
> > >> +
> > >> +    /* Skip unimplemented BARs and the upper half of 64bit BARS. */
> > >> +    if (!bar->size) {
> > >> +        return 0;
> > >> +    }
> > >> +
> > >> +    addr_lo = pci_default_read_config(pdev, PCI_BASE_ADDRESS_0 + nr * 
> > >> 4, 4);
> > >> +
> > >> +    addr_lo = addr_lo & (bar->ioport ? PCI_BASE_ADDRESS_IO_MASK :
> > >> +                                       PCI_BASE_ADDRESS_MEM_MASK);  
> > > 
> > > Nit, &= or combine with previous set.
> > >   
> > >> +    if (bar->type == PCI_BASE_ADDRESS_MEM_TYPE_64) {
> > >> +        addr_hi = pci_default_read_config(pdev,
> > >> +                                         PCI_BASE_ADDRESS_0 + (nr + 1) 
> > >> * 4, 4);
> > >> +    }
> > >> +
> > >> +    addr = ((uint64_t)addr_hi << 32) | addr_lo;  
> > > 
> > > Could we use a union?
> > >   
> > >> +
> > >> +    if (!QEMU_IS_ALIGNED(addr, bar->size)) {
> > >> +        return -EINVAL;
> > >> +    }  
> > > 
> > > What specifically are we validating here?  This should be true no
> > > matter what we wrote to the BAR or else BAR emulation is broken.  The
> > > bits that could make this unaligned are not implemented in the BAR.
> > >   
> > >> +
> > >> +    return 0;
> > >> +}
> > >> +
> > >> +static int vfio_bars_validate(VFIOPCIDevice *vdev)
> > >> +{
> > >> +    int i, ret;
> > >> +
> > >> +    for (i = 0; i < PCI_ROM_SLOT; i++) {
> > >> +        ret = vfio_bar_validate(vdev, i);
> > >> +        if (ret) {
> > >> +            error_report("vfio: BAR address %d validation failed", i);
> > >> +            return ret;
> > >> +        }
> > >> +    }
> > >> +    return 0;
> > >> +}
> > >> +
> > >>   static void vfio_bar_register(VFIOPCIDevice *vdev, int nr)
> > >>   {
> > >>       VFIOBAR *bar = &vdev->bars[nr];
> > >> @@ -2414,11 +2459,129 @@ static Object *vfio_pci_get_object(VFIODevice 
> > >> *vbasedev)
> > >>       return OBJECT(vdev);
> > >>   }
> > >>   
> > >> +static void vfio_pci_save_config(VFIODevice *vbasedev, QEMUFile *f)
> > >> +{
> > >> +    VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice, 
> > >> vbasedev);
> > >> +    PCIDevice *pdev = &vdev->pdev;
> > >> +    uint16_t pci_cmd;
> > >> +    int i;
> > >> +
> > >> +    for (i = 0; i < PCI_ROM_SLOT; i++) {
> > >> +        uint32_t bar;
> > >> +
> > >> +        bar = pci_default_read_config(pdev, PCI_BASE_ADDRESS_0 + i * 4, 
> > >> 4);
> > >> +        qemu_put_be32(f, bar);
> > >> +    }
> > >> +
> > >> +    qemu_put_be32(f, vdev->interrupt);
> > >> +    if (vdev->interrupt == VFIO_INT_MSI) {
> > >> +        uint32_t msi_flags, msi_addr_lo, msi_addr_hi = 0, msi_data;
> > >> +        bool msi_64bit;
> > >> +
> > >> +        msi_flags = pci_default_read_config(pdev, pdev->msi_cap + 
> > >> PCI_MSI_FLAGS,
> > >> +                                            2);
> > >> +        msi_64bit = (msi_flags & PCI_MSI_FLAGS_64BIT);
> > >> +
> > >> +        msi_addr_lo = pci_default_read_config(pdev,
> > >> +                                         pdev->msi_cap + 
> > >> PCI_MSI_ADDRESS_LO, 4);
> > >> +        qemu_put_be32(f, msi_addr_lo);
> > >> +
> > >> +        if (msi_64bit) {
> > >> +            msi_addr_hi = pci_default_read_config(pdev,
> > >> +                                             pdev->msi_cap + 
> > >> PCI_MSI_ADDRESS_HI,
> > >> +                                             4);
> > >> +        }
> > >> +        qemu_put_be32(f, msi_addr_hi);
> > >> +
> > >> +        msi_data = pci_default_read_config(pdev,
> > >> +                pdev->msi_cap + (msi_64bit ? PCI_MSI_DATA_64 : 
> > >> PCI_MSI_DATA_32),
> > >> +                2);
> > >> +        qemu_put_be32(f, msi_data);  
> > > 
> > > Isn't the data field only a u16?
> > >   
> > 
> > Yes, fixing it.
> > 
> > >> +    } else if (vdev->interrupt == VFIO_INT_MSIX) {
> > >> +        uint16_t offset;
> > >> +
> > >> +        /* save enable bit and maskall bit */
> > >> +        offset = pci_default_read_config(pdev,
> > >> +                                       pdev->msix_cap + PCI_MSIX_FLAGS 
> > >> + 1, 2);
> > >> +        qemu_put_be16(f, offset);
> > >> +        msix_save(pdev, f);
> > >> +    }
> > >> +    pci_cmd = pci_default_read_config(pdev, PCI_COMMAND, 2);
> > >> +    qemu_put_be16(f, pci_cmd);
> > >> +}
> > >> +
> > >> +static int vfio_pci_load_config(VFIODevice *vbasedev, QEMUFile *f)
> > >> +{
> > >> +    VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice, 
> > >> vbasedev);
> > >> +    PCIDevice *pdev = &vdev->pdev;
> > >> +    uint32_t interrupt_type;
> > >> +    uint32_t msi_flags, msi_addr_lo, msi_addr_hi = 0, msi_data;
> > >> +    uint16_t pci_cmd;
> > >> +    bool msi_64bit;
> > >> +    int i, ret;
> > >> +
> > >> +    /* retore pci bar configuration */
> > >> +    pci_cmd = pci_default_read_config(pdev, PCI_COMMAND, 2);
> > >> +    vfio_pci_write_config(pdev, PCI_COMMAND,
> > >> +                        pci_cmd & (!(PCI_COMMAND_IO | 
> > >> PCI_COMMAND_MEMORY)), 2);
> > >> +    for (i = 0; i < PCI_ROM_SLOT; i++) {
> > >> +        uint32_t bar = qemu_get_be32(f);
> > >> +
> > >> +        vfio_pci_write_config(pdev, PCI_BASE_ADDRESS_0 + i * 4, bar, 4);
> > >> +    }
> > >> +
> > >> +    ret = vfio_bars_validate(vdev);
> > >> +    if (ret) {
> > >> +        return ret;
> > >> +    }
> > >> +
> > >> +    interrupt_type = qemu_get_be32(f);
> > >> +
> > >> +    if (interrupt_type == VFIO_INT_MSI) {
> > >> +        /* restore msi configuration */
> > >> +        msi_flags = pci_default_read_config(pdev,
> > >> +                                            pdev->msi_cap + 
> > >> PCI_MSI_FLAGS, 2);
> > >> +        msi_64bit = (msi_flags & PCI_MSI_FLAGS_64BIT);
> > >> +
> > >> +        vfio_pci_write_config(pdev, pdev->msi_cap + PCI_MSI_FLAGS,
> > >> +                              msi_flags & (!PCI_MSI_FLAGS_ENABLE), 2);
> > >> +
> > >> +        msi_addr_lo = qemu_get_be32(f);
> > >> +        vfio_pci_write_config(pdev, pdev->msi_cap + PCI_MSI_ADDRESS_LO,
> > >> +                              msi_addr_lo, 4);
> > >> +
> > >> +        msi_addr_hi = qemu_get_be32(f);
> > >> +        if (msi_64bit) {
> > >> +            vfio_pci_write_config(pdev, pdev->msi_cap + 
> > >> PCI_MSI_ADDRESS_HI,
> > >> +                                  msi_addr_hi, 4);
> > >> +        }
> > >> +        msi_data = qemu_get_be32(f);
> > >> +        vfio_pci_write_config(pdev,
> > >> +                pdev->msi_cap + (msi_64bit ? PCI_MSI_DATA_64 : 
> > >> PCI_MSI_DATA_32),
> > >> +                msi_data, 2);
> > >> +
> > >> +        vfio_pci_write_config(pdev, pdev->msi_cap + PCI_MSI_FLAGS,
> > >> +                              msi_flags | PCI_MSI_FLAGS_ENABLE, 2);
> > >> +    } else if (interrupt_type == VFIO_INT_MSIX) {
> > >> +        uint16_t offset = qemu_get_be16(f);
> > >> +
> > >> +        /* load enable bit and maskall bit */
> > >> +        vfio_pci_write_config(pdev, pdev->msix_cap + PCI_MSIX_FLAGS + 1,
> > >> +                              offset, 2);
> > >> +        msix_load(pdev, f);
> > >> +    }
> > >> +    pci_cmd = qemu_get_be16(f);
> > >> +    vfio_pci_write_config(pdev, PCI_COMMAND, pci_cmd, 2);
> > >> +    return 0;
> > >> +}  
> > > 
> > > It always seems like there should be a lot more state than this, and I
> > > probably sound like a broken record because I ask every time, but maybe
> > > that's a good indication that we (or at least I) need a comment
> > > explaining why we only care about these.  For example, what if we
> > > migrate a device in the D3 power state, don't we need to account for
> > > the state stored in the PM capability or does the device wake up into
> > > D0 auto-magically after migration?  I think we could repeat that
> > > question for every capability that can be modified.  Even for the MSI/X
> > > cases, the interrupt may not be active, but there could be state in
> > > virtual config space that would be different on the target.  For
> > > example, if we migrate with a device in INTx mode where the guest had
> > > written vector fields on the source, but only writes the enable bit on
> > > the target, can we seamlessly figure out the rest?  For other
> > > capabilities, that state may represent config space changes written
> > > through to the physical device and represent a functional difference on
> > > the target.  Thanks,
> > >  
> > 
> > These are very basic set of registers from config state. Other are more 
> > of vendor specific which vendor driver can save and restore in their own 
> > data. I don't think we have to take care of all those vendor specific 
> > fields here.
> 
> That had not been clear to me.  Intel folks, is this your understanding
> regarding the responsibility of the user to save and restore config
> space of the device as part of the vendor provided migration stream
> data?  Thanks,
> 
Currently, the code works for us. but I agree with you that there should
be more states to save, at least for emulated config bits.
I think we should call pci_device_save() to serve that purpose.

Thanks
Yan