Re: [PATCHv8 00/11] Linear Address Masking enabling

[Jacob Pan]

Hi Dave,

On Mon, 12 Sep 2022 14:41:56 -0700, Dave Hansen <dave.hansen@xxxxxxxxx>
wrote:

> On 9/12/22 13:39, Jacob Pan wrote:
> >>> +	if (pasid_valid(mm->pasid) && !forced) {  
> > I don't think this works since we have lazy pasid free.  for example,
> > after all the devices did sva_unbind, mm->pasid  we'll remain valid
> > until mmdrop(). LAM  should be supported in this case.  
> 
> Nah, it works fine.
> It just means that the rules are "you can't do LAM if your process
> *EVER* got a PASID" instead of "you can't do LAM if you are actively
> using your PASID".
Sure it works if you change the rules, but this case need to documented.

> 
> We knew that PASID use would be a one-way trip for a process when we
> moved to the simplified implementation.  This is just more fallout from
> that.  It's fine.
> 
Is LAM also a one-way trip?

> > Perhaps, we could introduce another prctl flag for SVA, PR_GET_SVA?
> > Both iommu driver and LAM can set/query the flag. LAM applications may
> > not be the only ones want to know if share virtual addressing is  on.  
> 
> I don't think it's a good idea to add yet more UABI around this issue.
> Won't the IOMMU folks eventually get their hardware in line with LAM?
> Isn't this situation temporary?


Thanks,

Jacob