Upon cell creation, the ROOT_COS CBM is shrinked to prevent overlap
between the ROOT_COS CBM and the CBM of the newly created cell. Here,
the new ROOT_COS CBM is prevented from becoming empty, and in doing so,
the ROOT_COS CBM potentially moves to free bits.
There are two additional situations that need to be reflected by the
code:
1. It is possible that bits which are listed as 'freed' are also taken
by the newly created cell. Given that the freed_mask is not yet updated
with the newly created cell, it should be checked explicitly whether the
freed cells prevent the ROOT_COS CBM from becoming empty after moving to
the freed bits.
2. Even if the ROOT_COS CBM is not going empty, it might still overlap
with the newly created cell. Hence, moving to free bits should not skip
the shrinking, in the else clause.
A minimal example to demostrate this bug for a 10-way (bit) CBM:
jailhouse enable: creates a root cell with COS0 and CBM 3FF
jailhouse cell create: creates cell1 with COS1 and CBM 1F0
The free bits are now 20F, but as the CBM has to be contiguous, the
root cell has CBM 200. Free bits are 00F.
jailhouse cell create: creates cell2 with COS2 and CBM 3FC
Cell cell2 requires the top most bit (200), hence the root COS CBM
takes free bits 00F.
BUG: Root COS CBM gets bits 00F, overlapping with COS2
FIX: Root COS CBM is shrinked to 003, preventing overlap with the new
cell cell2.
Fixes: 3f04eb1753bb ("x86: Introduce Cache Allocation Technology support
for Intel CPUs")
Signed-off-by: Bram Hooimeijer <[email protected]>
---
hypervisor/arch/x86/cat.c | 53 +++++++++++++++++++++------------------
1 file changed, 28 insertions(+), 25 deletions(-)
diff --git a/hypervisor/arch/x86/cat.c b/hypervisor/arch/x86/cat.c
index f4c6f5d6..c91560a2 100644
--- a/hypervisor/arch/x86/cat.c
+++ b/hypervisor/arch/x86/cat.c
@@ -105,32 +105,35 @@ static bool shrink_root_cell_mask(u64 cell_mask)
root_cell.arch.cat_mask = 0;
merge_freed_mask_to_root();
- } else {
- /* Shrink the root cell's mask. */
- root_cell.arch.cat_mask &= ~cell_mask;
+ /* Check again, as freed bits might also be in cell_mask */
+ if ((root_cell.arch.cat_mask & ~cell_mask) == 0)
+ return false;
+ }
+ /* Shrink the root cell's mask. Might still be required if freed
+ * bits overlap with new mask. */
+ root_cell.arch.cat_mask &= ~cell_mask;
- /*
- * Ensure that the root mask is still contiguous:
- *
- * Check if taking out the new cell's mask from the root mask
- * created two halves there. Then shrink the root mask
- * additionally by the lower half and add that part to the
- * freed mask.
- *
- * Always removing the lower half simplifies this algorithm at
- * the price of possibly choosing the smaller sub-mask. Cell
- * configurations can avoid this by locating non-root cell
- * masks at the beginning of the L3 cache.
- */
- lo_mask_start = ffsl(root_cell.arch.cat_mask);
- lo_mask_len = ffzl(root_cell.arch.cat_mask >> lo_mask_start);
- lo_mask = BIT_MASK(lo_mask_start + lo_mask_len - 1,
- lo_mask_start);
-
- if (root_cell.arch.cat_mask & ~lo_mask) {
- root_cell.arch.cat_mask &= ~lo_mask;
- freed_mask |= lo_mask;
- }
+ /*
+ * Ensure that the root mask is still contiguous:
+ *
+ * Check if taking out the new cell's mask from the root mask
+ * created two halves there. Then shrink the root mask
+ * additionally by the lower half and add that part to the
+ * freed mask.
+ *
+ * Always removing the lower half simplifies this algorithm at
+ * the price of possibly choosing the smaller sub-mask. Cell
+ * configurations can avoid this by locating non-root cell
+ * masks at the beginning of the L3 cache.
+ */
+ lo_mask_start = ffsl(root_cell.arch.cat_mask);
+ lo_mask_len = ffzl(root_cell.arch.cat_mask >> lo_mask_start);
+ lo_mask = BIT_MASK(lo_mask_start + lo_mask_len - 1,
+ lo_mask_start);
+
+ if (root_cell.arch.cat_mask & ~lo_mask) {
+ root_cell.arch.cat_mask &= ~lo_mask;
+ freed_mask |= lo_mask;
}
/* Cells using the root COS are also affected by shrinking. */
--
2.28.0
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