On Wed, Aug 15, 2018 at 01:26:31PM +0100, Robin Murphy wrote: > On 15/08/18 11:23, Zhen Lei wrote: > >The condition "(int)(VAL - sync_idx) >= 0" to break loop in function > >__arm_smmu_sync_poll_msi requires that sync_idx must be increased > >monotonously according to the sequence of the CMDs in the cmdq. > > > >But ".msidata = atomic_inc_return_relaxed(&smmu->sync_nr)" is not protected > >by spinlock, so the following scenarios may appear: > >cpu0 cpu1 > >msidata=0 > > msidata=1 > > insert cmd1 > >insert cmd0 > > smmu execute cmd1 > >smmu execute cmd0 > > poll timeout, because msidata=1 is overridden by > > cmd0, that means VAL=0, sync_idx=1. > > > >This is not a functional problem, just make the caller wait for a long > >time until TIMEOUT. It's rare to happen, because any other CMD_SYNCs > >during the waiting period will break it. > > > >Signed-off-by: Zhen Lei <[email protected]> > >--- > > drivers/iommu/arm-smmu-v3.c | 12 ++++++++---- > > 1 file changed, 8 insertions(+), 4 deletions(-) > > > >diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c > >index 1d64710..3f5c236 100644 > >--- a/drivers/iommu/arm-smmu-v3.c > >+++ b/drivers/iommu/arm-smmu-v3.c > >@@ -566,7 +566,7 @@ struct arm_smmu_device { > > > > int gerr_irq; > > int combined_irq; > >- atomic_t sync_nr; > >+ u32 sync_nr; > > > > unsigned long ias; /* IPA */ > > unsigned long oas; /* PA */ > >@@ -775,6 +775,11 @@ static int queue_remove_raw(struct arm_smmu_queue *q, > >u64 *ent) > > return 0; > > } > > > >+static inline void arm_smmu_cmdq_sync_set_msidata(u64 *cmd, u32 msidata) > > If we *are* going to go down this route then I think it would make sense to > move the msiaddr and CMDQ_SYNC_0_CS_MSI logic here as well; i.e. > arm_smmu_cmdq_build_cmd() always generates a "normal" SEV-based sync > command, then calling this guy would convert it to an MSI-based one. As-is, > having bits of mutually-dependent data handled across two separate places > just seems too messy and error-prone.
Yeah, but I'd first like to see some number showing that doing all of this under the lock actually has an impact. Will _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
