On Sat, 9 May 2020, Julien Grall wrote: > Hi Stefano, > > On 09/05/2020 01:07, Stefano Stabellini wrote: > > On Fri, 1 May 2020, Julien Grall wrote: > > > On 01/05/2020 02:26, Stefano Stabellini wrote: > > > > On Wed, 15 Apr 2020, Julien Grall wrote: > > > > > Hi Stefano, > > > > > > > > > > On 15/04/2020 02:02, Stefano Stabellini wrote: > > > > > > We always use a fix address to map the vPL011 to domains. The > > > > > > address > > > > > > could be a problem for domains that are directly mapped. > > > > > > > > > > > > Instead, for domains that are directly mapped, reuse the address of > > > > > > the > > > > > > physical UART on the platform to avoid potential clashes. > > > > > > > > > > How do you know the physical UART MMIO region is big enough to fit the > > > > > PL011? > > > > > > > > That cannot be because the vPL011 MMIO size is 1 page, which is the > > > > minimum right? > > > > > > No, there are platforms out with multiple UARTs in the same page (see > > > sunxi > > > for instance). > > > > But if there are multiple UARTs sharing the same page, and the first one > > is used by Xen, there is no way to assign one of the secondary UARTs to > > a domU. So there would be no problem choosing the physical UART address > > for the virtual PL011. > > AFAICT, nothing prevents a user to assign such UART to a dom0less guest today. > It would not be safe, but it should work. > > If you want to make it safe, then you would need to trap the MMIO access so > they can be sanitized. For a UART device, I don't think the overhead would be > too bad. > > Anyway, the only thing I request is to add sanity check in the code to help > the user diagnostics any potential clash.
OK thanks for clarifying, I'll do that.
