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> u128 data128[2]; > }; > }; > > And don't make a new type. IIRC the cmpxchg likes to have alignment > and the u128 provides that.. OK. >> +static void update_dte256(struct amd_iommu *iommu, u16 devid, struct dte256 *new) >> +{ >> + struct dev_table_entry *dev_table = get_dev_table(iommu); >> + struct dte256 *ptr = (struct dte256 *)&dev_table[devid]; >> + struct dte256 old = { >> + .qw_lo.data = ptr->qw_lo.data, >> + .qw_hi.data = ptr->qw_hi.data, >> + }; >> + >> + /* Update qw_lo */ >> + if (!try_cmpxchg128(&ptr->qw_lo.data, &old.qw_lo.data, new->qw_lo.data)) >> + goto err_out; >> + >> + /* Update qw_hi */ >> + if (!try_cmpxchg128(&ptr->qw_hi.data, &old.qw_hi.data, new->qw_hi.data)) { >> + /* Restore qw_lo */ >> + try_cmpxchg128(&ptr->qw_lo.data, &new->qw_lo.data, old.qw_lo.data); >> + goto err_out; >> + } > > I don't think this is going to work like this, the interrupt remapping > code can asynchronously change the values (it is an existing race bug) > and if it races that will cause these to fail too, and this doesn't > handle that case at all. > > IMHO the simple solution would hold the spinlock and transfer the > interrupt remapping fields then directly write them without a failable > cmpxchg. Maybe you could also use a cmpxchg loop to transfer the interrupt > remapping bits without a lock.. OK, I'll as synchronization when updating DTE. > Can you assume cmpxchg 128 is available on all CPUs that have the > iommu? I see google says some early AMD 64 bit CPUs don't have it? Do > they have iommu's? I had wondered if the doc intended that some 128 > bit SSE/MMX store store would be used here?? > > If cmpxchg128 is safe checking that cap and refusing to probe the > iommu driver would be appropriate. Otherwise a 64 bit flow still has > to work? According to the AMD BIOS and Kernel Developer's Guide (BDKG) dated back since family 10h Processor (https://www.amd.com/content/dam/amd/en/documents/archived-tech-docs/programmer-references/31116.pdf), which is the first introduction of AMD IOMMU, AMD processor always support for CPUID Fn0000_0001_ECX[CMPXCHG16B]=1. So, it should be safe to assume that cmpxchg128 is available with all AMD processor w/ IOMMU. > Finally, the order of programming the two 128s depends on what you are > programming. The first 128 contains the valid bit so you shouldn't be > writing the second 128 after, and vice versa. This will make > undesirable races around Guest Paging Mode and eventually viommuen at > least. Ok, I'll program the higher 128-bit first. > If you have to solve the 64 bit case too, then you really should use > the programmer from SMMUv3. Everyone seems to need this logic and it > should be generalized. I can help you do it.. I have a patch to make > that logic use 128 bit stores too someplace. > > Otherwise you can possibly open code the 128 bit path with some more > care to check the valid bits and set the order, plus the interrupt > remapping locking. I think the cmpxchg128 should still work and would be a simpler solution. I am sending out v2 shortly. Thanks, Suravee