Re: [PATCH v2 0/2] Add API for making parts of a MMIO page R/O and use it in XHCI console

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Fri, May 5, 2023 at 5:26 PM Marek Marczykowski-Górecki
<marmarek@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> On older systems, XHCI xcap had a layout that no other (interesting) registers
> were placed on the same page as the debug capability, so Linux was fine with
> making the whole page R/O. But at least on Tiger Lake and Alder Lake, Linux
> needs to write to some other registers on the same page too.
>
> Add a generic API for making just parts of an MMIO page R/O and use it to fix
> USB3 console with share=yes or share=hwdom options. More details in commit
> messages.
>
> Marek Marczykowski-Górecki (2):
>   x86/mm: add API for marking only part of a MMIO page read only
>   drivers/char: Use sub-page ro API to make just xhci dbc cap RO

Series:
Tested-by: Jason Andryuk <jandryuk@xxxxxxxxx>

I had the issue with a 10th Gen, Comet Lake, laptop.  With an HVM
usbvm with dbgp=xhci,share=1, Xen crashed the domain because of:
(XEN) d1v0 EPT violation 0xdaa (-w-/r-x) gpa 0x000000f1008470 mfn 0xcc328 type 5

The BAR is mfn 0xcc320-0xcc32f

Booting PV, it faulted at drivers/usb/host/pci-quirks.c:1170 which looks to be:
```
/* Disable any BIOS SMIs and clear all SMI events*/
writel(val, base + ext_cap_offset + XHCI_LEGACY_CONTROL_OFFSET);
```

Thanks for integrating XUE, Marek!

Regards,
Jason