From: Alexey Kardashevskiy aik@ozlabs.ru
commit 56090a3902c80c296e822d11acdb6a101b322c52 upstream.
pnv_tce() returns a pointer to a TCE entry and originally a TCE table would be pre-allocated. For the default case of 2GB window the table needs only a single level and that is fine. However if more levels are requested, it is possible to get a race when 2 threads want a pointer to a TCE entry from the same page of TCEs.
This adds cmpxchg to handle the race. Note that once TCE is non-zero, it cannot become zero again.
Fixes: a68bd1267b72 ("powerpc/powernv/ioda: Allocate indirect TCE levels on demand") CC: stable@vger.kernel.org # v4.19+ Signed-off-by: Alexey Kardashevskiy aik@ozlabs.ru Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20190718051139.74787-2-aik@ozlabs.ru Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/platforms/powernv/pci-ioda-tce.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-)
--- a/arch/powerpc/platforms/powernv/pci-ioda-tce.c +++ b/arch/powerpc/platforms/powernv/pci-ioda-tce.c @@ -49,6 +49,9 @@ static __be64 *pnv_alloc_tce_level(int n return addr; }
+static void pnv_pci_ioda2_table_do_free_pages(__be64 *addr, + unsigned long size, unsigned int levels); + static __be64 *pnv_tce(struct iommu_table *tbl, bool user, long idx, bool alloc) { __be64 *tmp = user ? tbl->it_userspace : (__be64 *) tbl->it_base; @@ -58,9 +61,9 @@ static __be64 *pnv_tce(struct iommu_tabl
while (level) { int n = (idx & mask) >> (level * shift); - unsigned long tce; + unsigned long oldtce, tce = be64_to_cpu(READ_ONCE(tmp[n]));
- if (tmp[n] == 0) { + if (!tce) { __be64 *tmp2;
if (!alloc) @@ -71,10 +74,15 @@ static __be64 *pnv_tce(struct iommu_tabl if (!tmp2) return NULL;
- tmp[n] = cpu_to_be64(__pa(tmp2) | - TCE_PCI_READ | TCE_PCI_WRITE); + tce = __pa(tmp2) | TCE_PCI_READ | TCE_PCI_WRITE; + oldtce = be64_to_cpu(cmpxchg(&tmp[n], 0, + cpu_to_be64(tce))); + if (oldtce) { + pnv_pci_ioda2_table_do_free_pages(tmp2, + ilog2(tbl->it_level_size) + 3, 1); + tce = oldtce; + } } - tce = be64_to_cpu(tmp[n]);
tmp = __va(tce & ~(TCE_PCI_READ | TCE_PCI_WRITE)); idx &= ~mask;