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    Subject[PATCH 4.14 18/69] xen/pciback: Dont disable PCI_COMMAND on PCI device reset.
    Date
    From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

    commit 7681f31ec9cdacab4fd10570be924f2cef6669ba upstream.

    There is no need for this at all. Worst it means that if
    the guest tries to write to BARs it could lead (on certain
    platforms) to PCI SERR errors.

    Please note that with af6fc858a35b90e89ea7a7ee58e66628c55c776b
    "xen-pciback: limit guest control of command register"
    a guest is still allowed to enable those control bits (safely), but
    is not allowed to disable them and that therefore a well behaved
    frontend which enables things before using them will still
    function correctly.

    This is done via an write to the configuration register 0x4 which
    triggers on the backend side:
    command_write
    \- pci_enable_device
    \- pci_enable_device_flags
    \- do_pci_enable_device
    \- pcibios_enable_device
    \-pci_enable_resourcess
    [which enables the PCI_COMMAND_MEMORY|PCI_COMMAND_IO]

    However guests (and drivers) which don't do this could cause
    problems, including the security issues which XSA-120 sought
    to address.

    Reported-by: Jan Beulich <jbeulich@suse.com>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Reviewed-by: Prarit Bhargava <prarit@redhat.com>
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/xen/xen-pciback/pciback_ops.c | 2 --
    1 file changed, 2 deletions(-)

    --- a/drivers/xen/xen-pciback/pciback_ops.c
    +++ b/drivers/xen/xen-pciback/pciback_ops.c
    @@ -127,8 +127,6 @@ void xen_pcibk_reset_device(struct pci_d
    if (pci_is_enabled(dev))
    pci_disable_device(dev);

    - pci_write_config_word(dev, PCI_COMMAND, 0);
    -
    dev->is_busmaster = 0;
    } else {
    pci_read_config_word(dev, PCI_COMMAND, &cmd);

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