Re: [PATCH v13] PCI: Add device-specific reset for Qualcomm devices

[Bjorn Helgaas]

On Thu, Sep 17, 2026 at 08:59:18AM +0200, Jose Ignacio Tornos Martinez wrote:
> Hi Bjorn,
> 
> Thanks for the review.
> 
> > I guess you are saying that some kind of reset *does* work
> > fine in normal, clean VM termination?  If reset works fine
> > for normal VM termination but not for VM crash, do we have
> > any idea why they are different?
>
> It depends on the device:
> 
> - For the modems (SDX62/SDX65), without a proper reset
>   capability, these devices never successfully initialize
>   even on first VM assignment.
> 
> - For the WLAN devices (WCN6855/WCN7850), the reset fails
>   in both cases, but on clean VM shutdown the guest driver's
>   .shutdown/.remove callbacks properly deinitialize the device
>   (stop DMA, disable interrupts, etc.), so it ends up in a
>   known-good state even without a successful reset. On unclean
>   termination (crash, force-off), the guest driver callbacks
>   never run, the device stays in an undefined state, and
>   without a working reset it cannot be reused.

Ah, so this depends on the previous VM tenant to clean up after itself
instead of the host kernel enforcing the isolation?

That seems important to mention and potentially unacceptable to
tenants if an issue in the tenant's kernel may cause their data to be
leaked to the next user of the device.

> I will try to clarify this better in the commit messages for v14.
> 
> > Since these basically copy code from other drivers, is there
> > an opportunity to remove it from those drivers and use this
> > instead?
>
> Yes, that could be a follow-up after this lands.

Sounds good.