RE: [RFC PATCH] scsi: qla2xxx: Use the real INTx pin for the port number on Hyper-V guests

[Michael Kelley <mhklinux@outlook.com>]

From: Laurence Oberman <loberman@redhat.com> Sent: Wednesday, November 4, 2026 2:26 PM
> 
> qla2x00_set_isp_flags() derives the physical port number from
> PCI_INTERRUPT_PIN, and the port number selects the per-port VPD, NVRAM,
> NPIV and FCP priority flash regions.
> 
> On Hyper-V guests, pci-hyperv returns 0 for byte and word reads of
> PCI_INTERRUPT_PIN since commit fea93a3e5d5e ("PCI: hv: Return zero, not
> garbage, when reading PCI_INTERRUPT_PIN"). Commit 7268e509b43a ("scsi:
> qla2xxx: Handle INTx not connected while passing through") then falls
> back to PCI_FUNC(). With Discrete Device Assignment (DDA), each function
> of a multi-port HBA is presented as function 0 in its own PCI domain, so
> every port gets port_no 0. All ports read port 0's NVRAM, pass the
> checksum and register the same WWPN, and nothing is logged.
> 
> Without that commit, port_no underflows to 255, no flash region is
> selected and every port fails with "Inconsistent NVRAM checksum" and
> falls back to the default WWPN.
> 
> pci-hyperv only zeroes byte and word accesses within 0x3c-0x3d. A dword
> read at PCI_INTERRUPT_LINE reaches the device's config space and returns
> the real pin in bits 15:8. On Hyper-V guests, use that when the byte
> read returns 0, and warn if the pin is still 0 so that duplicate WWPNs
> are not silent. Bare metal, KVM/vfio and other hypervisors are
> unchanged.

There's a patch in flight [1] that kills the behavior that your patch takes
advantage of. I don't have knowledge of the full details that motivated [1],
so maybe Mukesh Rathor or Wei Liu can add some info, as well as
comment on the validity of what you are observing as a possible
work-around to the qla2xxx problem.

Michael

[1] https://lore.kernel.org/linux-hyperv/20260913232255.2801797-1-wei.liu@kernel.org/

> 
> Tested with an equivalent change on a RHEL 9 (5.14-based) guest with a
> dual-port QLE2692 (ISP2261) assigned through DDA (Hyper-V host
> 10.0.17763):
> 
>   before: both ports "Inconsistent NVRAM checksum=0xffffffc0 id=NGKP",
>           both WWPN 0x210000e08b1c5586
>   after:  port_no 1 and 0, NVRAM valid, WWPN 0x210034800d7065bd and
>           0x210034800d7065bc, fabric login and FC-NVMe localport
>           registration on both ports
> 
> Also tested on bare metal (ISP2031): the new path is not taken and port
> numbers and WWPNs are unchanged.
> 
> Signed-off-by: Laurence Oberman <loberman@redhat.com>
> ---
> RFC: this relies on pci-hyperv not virtualizing dword reads at 0x3c,
> which is an implementation detail rather than an interface. It is posted
> as the smallest working fix and to start the discussion. Feedback wanted
> on cleaner alternatives:
> 
>  - Hyper-V (linux-hyperv): could pci-hyperv expose the real
>    PCI_INTERRUPT_PIN, or provide the physical function number, for DDA
>    devices? Some drivers use the pin for port identity, not only for
>    interrupt routing.
> 
>  - Marvell: is there a firmware or register source for the physical
>    port that does not depend on PCI config space? CSRX_FUNCTION in
>    ctrl_status is a single bit and would not cover quad-port
>    27xx/28xx/29xx.
> 
>  - The check is x86-only (hypervisor_is_type()). pci-hyperv also
>    supports arm64 guests; a better way to detect a pci-hyperv bus is
>    welcome.
> 
> This has not yet been tested on a 7.3 kernel in the DDA guest; testing
> was on a RHEL 9.8 backport. The upstream behaviour without this patch
> (duplicate WWPNs with no warning) follows from the code and has not yet
> been reproduced on 7.3.
> 
>  drivers/scsi/qla2xxx/qla_os.c | 40 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
> index 3c412c7fb6fe..4180d3f15231 100644
> --- a/drivers/scsi/qla2xxx/qla_os.c
> +++ b/drivers/scsi/qla2xxx/qla_os.c
> @@ -24,6 +24,10 @@
>  #include <scsi/scsi_transport.h>
>  #include <scsi/scsi_transport_fc.h>
> 
> +#ifdef CONFIG_X86
> +#include <asm/hypervisor.h>
> +#endif
> +
>  #include "qla_target.h"
> 
>  /*
> @@ -2704,6 +2708,40 @@ static struct isp_operations qla29xx_isp_ops = {
>  	.initialize_adapter	= qla2x00_initialize_adapter,
>  };
> 
> +/*
> + * Read the INTx pin used to derive the physical port number.
> + *
> + * pci-hyperv hard-wires byte and word reads of PCI_INTERRUPT_PIN to zero.
> + * With Hyper-V Discrete Device Assignment every function is also presented
> + * as function 0 in its own PCI domain, so the PCI_FUNC() fallback gives
> + * port 0 for every port and they all report port 0's WWPN. A dword read at
> + * PCI_INTERRUPT_LINE is not virtualized by pci-hyperv and returns the
> + * device's pin in bits 15:8, so use that on Hyper-V guests.
> + */
> +static u8
> +qla2x00_get_intx_pin(struct qla_hw_data *ha)
> +{
> +	u8 pin;
> +
> +	pci_read_config_byte(ha->pdev, PCI_INTERRUPT_PIN, &pin);
> +#ifdef CONFIG_X86
> +	if (!pin && hypervisor_is_type(X86_HYPER_MS_HYPERV)) {
> +		u32 val = 0;
> +
> +		pci_read_config_dword(ha->pdev, PCI_INTERRUPT_LINE, &val);
> +		pin = (val >> 8) & 0xff;
> +		if (pin)
> +			ql_log_pci(ql_log_info, ha->pdev, 0xffff,
> +				   "Hyper-V: INTx pin reads 0, config dword 0x%08x
> gives pin %u.\n",
> +				   val, pin);
> +		else
> +			ql_log_pci(ql_log_warn, ha->pdev, 0xffff,
> +				   "Hyper-V: unable to determine physical port, ports
> may report duplicate WWPNs.\n");
> +	}
> +#endif
> +	return pin;
> +}
> +
>  static inline void
>  qla2x00_set_isp_flags(struct qla_hw_data *ha)
>  {
> @@ -2887,7 +2925,7 @@ qla2x00_set_isp_flags(struct qla_hw_data *ha)
>  		ha->port_no = ha->portnum & 1;
>  	else {
>  		/* Get adapter physical port no from interrupt pin register. */
> -		pci_read_config_byte(ha->pdev, PCI_INTERRUPT_PIN, &ha->port_no);
> +		ha->port_no = qla2x00_get_intx_pin(ha);
>  		if (ha->port_no == 0) {
>  			/* None of INT[A|B|C|D] may be virtualized by vfio */
>  			ha->port_no = PCI_FUNC(ha->pdev->devfn);
> --
> 2.56.0
>