It isn't completely obvious why user page types do not have overlays applied in PIE_EL1. Add a comment to that effect, to avoid unpleasant surprises in the future.
Signed-off-by: Kevin Brodsky <[email protected]> --- arch/arm64/include/asm/pgtable-prot.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h index 212ce1b02e15..6e2f99820909 100644 --- a/arch/arm64/include/asm/pgtable-prot.h +++ b/arch/arm64/include/asm/pgtable-prot.h @@ -175,6 +175,13 @@ static inline bool __pure lpa2_is_enabled(void) PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_READONLY), PIE_R_O) | \ PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED), PIE_RW_O)) +/* + * Regular user page types such as _PAGE_SHARED must not have overlays applied + * in PIE_EL1. If POE is enabled at EL1, and in the absence of FEAT_LSUI, this + * would break futex atomic operations on user memory with a non-default + * POIndex; the privileged atomic load/store instructions would be mistakenly + * checked against POR_EL1. + */ #define PIE_E1 ( \ PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS), PIE_NONE_O) | \ PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS_RO), PIE_NONE_O) | \ -- 2.51.2
