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

[Laurence Oberman <loberman@redhat.com>]

On Thu, 2026-11-05 at 00:46 +0000, Michael Kelley wrote:
> 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
> > 
Hello Michael,

Thanks very much for the information. I will follow the thread. 
Our main pressing issue is any guest on HYPER-V with DDA moving to
RHEL9 from RHEL8 loses functionality for the pass-through qla2xxx ports

Regards
Laurence