2017-10-26 09:13+0200, Paolo Bonzini: > For many years some users of assigned devices have reported worse > performance on AMD processors with NPT than on AMD without NPT, > Intel or bare metal. > > The reason turned out to be that SVM is discarding the guest PAT > setting and uses the default (PA0=PA4=WB, PA1=PA5=WT, PA2=PA6=UC-, > PA3=UC). The guest might be using a different setting, and > especially might want write combining but isn't getting it > (instead getting slow UC or UC- accesses). > > Thanks a lot to geoff@xxxxxxxxxxxxxxx for noticing the relation > to the g_pat setting. The patch has been tested also by a bunch > of people on VFIO users forums. > > Fixes: 709ddebf81cb40e3c36c6109a7892e8b93a09464 > Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=196409 > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Applied, thanks.