Hi Peter, On Fri, Jul 19, 2024 at 04:57:18PM +0100, Peter Maydell wrote: > On Fri, 19 Jul 2024 at 16:36, Julien Grall <jul...@xen.org> wrote: > > > > Hi, > > > > On 18/07/2024 10:43, Julien Grall wrote: > > > Hi Eric, > > > > > > On 17/07/2024 18:43, Eric Auger wrote: > > >> Hi Peter, Richard, > > >> > > >> On 7/17/24 17:09, Jean-Philippe Brucker wrote: > > >>> On Mon, Jul 15, 2024 at 08:45:00AM +0000, Mostafa Saleh wrote: > > >>>> Currently, QEMU supports emulating either stage-1 or stage-2 SMMUs > > >>>> but not nested instances. > > >>>> This patch series adds support for nested translation in SMMUv3, > > >>>> this is controlled by property “arm-smmuv3.stage=nested”, and > > >>>> advertised to guests as (IDR0.S1P == 1 && IDR0.S2P == 2) > > >>> For the whole series (3-9, 11, 12, 15, 16, 18): > > >>> > > >>> Reviewed-by: Jean-Philippe Brucker <jean-phili...@linaro.org> > > >>> > > >>> (and I think patch 16 is missing Eric's R-b) > > >> > > >> Jean-Philippe and I have followed up the progress of this series, > > >> Mostafa took into account all our comments and all the patches were > > >> reviewed. It seems to be in a pretty decent state so if you don't have > > >> any objection, please consider pulling it for 9.1. > > >> > > >> On my end I did some testing in non nesting mode with virtio-net/vhost > > >> and I have not noticed any regression. > > >> Would be nice if someone could send his T-b for the nested part though > > >> (Julien?). > > > > > > I haven't yet tried the latest version. I will do that in the next > > > couple of days. > > I see this is already merged. If this still matters: > > > > Tested-by: Julien Grall <jgr...@amazon.com> > > We can't retrospectively add the tag, but the testing itself > is still important -- thanks for doing it. > > Q: is there any reason not to: > (a) change the default to "nested" rather than "1" > (b) make the virt board (for new virt machine versions) use > "nested"? > > AIUI "nested" should be a superset of "stage-1 only", the guest > can just ignore stage-2 if it doesn't care about it. Or is > there a performance hit from having stage-2 around even if the > guest doesn't enable it?
I didn’t do benchmarks, but from the code, I don’t think there would be a difference from using stage-1 only or nested stages with stage-1 config. I didn’t make “nested” the default stage or used it for the virt board, as I was worried about compatibility issues (I think that breaks backward migration), but otherwise I don’t see issues. But if I understand correctly, setting that for virt board 9.1 (virt_machine_9_1_options) would be fine? Thanks, Mostafa > > thanks > -- PMM
