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charset="us-ascii" Content-ID: <90F8CBDA3A0B90419D79D6E22F965BF5@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 93c80bad-9466-44db-ec75-08d7261bb347 X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Aug 2019 09:41:10.8038 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: MdxfRrT1tnirpMD7F4X4fVc/NF9eA4reAHiWJxZXC3WGTTkk7xhHICB8NDbLQrC2ceyRa9oGIDLyaB1IoFYdtg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1216 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-21_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=968 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908210104 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Aug 20, 2019, at 1:23 PM, Song Liu wrote: >=20 > Before 32-bit support, pti_clone_pmds() always adds PMD_SIZE to addr. > This behavior changes after the 32-bit support: pti_clone_pgtable() > increases addr by PUD_SIZE for pud_none(*pud) case, and increases addr by > PMD_SIZE for pmd_none(*pmd) case. However, this is not accurate because > addr may not be PUD_SIZE/PMD_SIZE aligned. >=20 > Fix this issue by properly rounding up addr to next PUD_SIZE/PMD_SIZE > in these two cases. After poking around more, I found the following doesn't really make=20 sense.=20 Sorry for the noise.=20 Song =20 >=20 > The following explains how we debugged this issue: >=20 > We use huge page for hot text and thus reduces iTLB misses. As we > benchmark 5.2 based kernel (vs. 4.16 based), we found ~2.5x more > iTLB misses. >=20 > To figure out the issue, I use a debug patch that dumps page table for > a pid. The following are information from the workload pid. >=20 > For the 4.16 based kernel: >=20 > host-4.16 # grep "x pmd" /sys/kernel/debug/page_tables/dump_pid > 0x0000000000600000-0x0000000000e00000 8M USR ro PSE = x pmd > 0xffffffff81a00000-0xffffffff81c00000 2M ro PSE = x pmd >=20 > For the 5.2 based kernel before this patch: >=20 > host-5.2-before # grep "x pmd" /sys/kernel/debug/page_tables/dump_pid > 0x0000000000600000-0x0000000000e00000 8M USR ro PSE = x pmd >=20 > The 8MB text in pmd is from user space. 4.16 kernel has 1 pmd for the > irq entry table; while 4.16 kernel doesn't have it. >=20 > For the 5.2 based kernel after this patch: >=20 > host-5.2-after # grep "x pmd" /sys/kernel/debug/page_tables/dump_pid > 0x0000000000600000-0x0000000000e00000 8M USR ro PSE = x pmd > 0xffffffff81000000-0xffffffff81e00000 14M ro PSE = GLB x pmd >=20 > So after this patch, the 5.2 based kernel has 7 PMDs instead of 1 PMD > in 4.16 kernel. This further reduces iTLB miss rate >=20 > Cc: stable@vger.kernel.org # v4.19+ > Fixes: 16a3fe634f6a ("x86/mm/pti: Clone kernel-image on PTE level for 32 = bit") > Reviewed-by: Rik van Riel > Signed-off-by: Song Liu > Cc: Joerg Roedel > Cc: Thomas Gleixner > Cc: Dave Hansen > Cc: Andy Lutomirski > Cc: Peter Zijlstra > --- > arch/x86/mm/pti.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c > index b196524759ec..1337494e22ef 100644 > --- a/arch/x86/mm/pti.c > +++ b/arch/x86/mm/pti.c > @@ -330,13 +330,13 @@ pti_clone_pgtable(unsigned long start, unsigned lon= g end, >=20 > pud =3D pud_offset(p4d, addr); > if (pud_none(*pud)) { > - addr +=3D PUD_SIZE; > + addr =3D round_up(addr + 1, PUD_SIZE); > continue; > } >=20 > pmd =3D pmd_offset(pud, addr); > if (pmd_none(*pmd)) { > - addr +=3D PMD_SIZE; > + addr =3D round_up(addr + 1, PMD_SIZE); > continue; > } >=20 > --=20 > 2.17.1 >=20