On Fri, Apr 23, 2021 at 02:01:19PM +0100, Peter Maydell wrote: > On Thu, 22 Apr 2021 at 23:24, Michael S. Tsirkin <m...@redhat.com> wrote: > > > > From: Jean-Philippe Brucker <jean-phili...@linaro.org> > > > > AMD IOMMU PTEs have a special mode allowing to specify an arbitrary page > > size. Quoting the AMD IOMMU specification: "When the Next Level bits [of > > a pte] are 7h, the size of the page is determined by the first zero bit > > in the page address, starting from bit 12." > > > > So if the lowest bits of the page address is 0, the page is 8kB. If the > > lowest bits are 011, the page is 32kB. Currently pte_override_page_mask() > > doesn't compute the right value for this page size and amdvi_translate() > > can return the wrong guest-physical address. With a Linux guest, DMA > > from SATA devices accesses the wrong memory and causes probe failure: > > > > qemu-system-x86_64 ... -device amd-iommu -drive id=hd1,file=foo.bin,if=none > > \ > > -device ahci,id=ahci -device ide-hd,drive=hd1,bus=ahci.0 > > [ 6.613093] ata1.00: qc timeout (cmd 0xec) > > [ 6.615062] ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4) > > > > Fix the page mask. > > > > Signed-off-by: Jean-Philippe Brucker <jean-phili...@linaro.org> > > Message-Id: <20210421084007.1190546-1-jean-phili...@linaro.org> > > Reviewed-by: Michael S. Tsirkin <m...@redhat.com> > > Signed-off-by: Michael S. Tsirkin <m...@redhat.com> > > Jean-Philippe, do you know if this is a regression since 5.2?
I don't think so, I can reproduce it with v5.2.0. > I'm guessing not given that the function in question has been that > way since the amd_iommu was introduced in 2016. There has been a lot of work on the AMD IOMMU driver in Linux recently. Maybe that exacerbated the problem but I can't find a relevant change. It's also possible that this path hasn't been exercised before - I just happened to run a SATA device under AMD IOMMU this week to debug an unrelated Linux issue. The other devices in the VM don't seem to have a problem doing DMA. Thanks, Jean
