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powerpc/powernv/ioda: Fix race in TCE level allocation

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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: a68bd1267b ("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
This commit is contained in:
Alexey Kardashevskiy 2019-07-18 15:11:36 +10:00 committed by Michael Ellerman
parent c784be435d
commit 56090a3902
1 changed files with 13 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
arch/powerpc/platforms/powernv/pci-ioda-tce.c
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@ -48,6 +48,9 @@ static __be64 *pnv_alloc_tce_level(int nid, unsigned int shift)
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;
@ -57,9 +60,9 @@ static __be64 *pnv_tce(struct iommu_table *tbl, bool user, long idx, bool alloc)
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)
@ -70,10 +73,15 @@ static __be64 *pnv_tce(struct iommu_table *tbl, bool user, long idx, bool alloc)
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;