Re: [PATCH 02/16] debug_vm_pgtable/ppc64: Avoid setting top bits in radom value
From: Aneesh Kumar K.V <hidden>
Date: 2020-08-12 06:43:51
Also in:
linux-mm
On 8/12/20 12:10 PM, Christophe Leroy wrote:
Le 12/08/2020 à 08:33, Aneesh Kumar K.V a écrit :quoted
ppc64 use bit 62 to indicate a pte entry (_PAGE_PTE). Avoid setting that bit in random value. Signed-off-by: Aneesh Kumar K.V <redacted> --- mm/debug_vm_pgtable.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c index 086309fb9b6f..4c32063a8acf 100644 --- a/mm/debug_vm_pgtable.c +++ b/mm/debug_vm_pgtable.c@@ -45,9 +45,12 @@* pxx_clear() because of how dynamic page table folding works on s390. So * while loading up the entries do not change the lower 4 bits. It does not * have affect any other platform. + * + * Also avoid the 62nd bit on ppc64 that is used to mark a pte entry. */ #define S390_MASK_BITS 4 -#define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS) +#define PPC_MASK_BITS 2 +#define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1 - PPC_MASK_BITS, S390_MASK_BITS)Do you mean: #define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1, PPC_MASK_BITS | S390_MASK_BITS)
IIUC GENMASK(hi, low) generate a mask from hi to low bits. Since i want to avoid bit 62, I am forcing it to generate bits from (61, 4) -aneesh