From: Björn Töpel <[email protected]>
The RISC-V port requires that kernel PGD entries are to be
synchronized between MMs. This is done via the vmalloc_fault()
function, that simply copies the PGD entries from init_mm to the
faulting one.
Historically, faulting in PGD entries have been a source for both bugs
[1], and poor performance.
One way to get rid of vmalloc faults is by pre-allocating the PGD
entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on
SV39). The pre-allocation function is pulled from Jörg Rödel's x86
work, with the addition of 3-level page tables (PMD allocations).
The pmd_alloc() function needs the ptlock cache to be initialized
(when split page locks is enabled), so the pre-allocation is done in a
RISC-V specific pgtable_cache_init() implementation.
Pre-allocate the kernel PGD entries for the vmalloc/modules area, but
only for 64b platforms.
Link: https://lore.kernel.org/lkml/[email protected]/ # [1]
Signed-off-by: Björn Töpel <[email protected]>
---
arch/riscv/mm/fault.c | 20 +++------------
arch/riscv/mm/init.c | 58 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 62 insertions(+), 16 deletions(-)
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 8685f85a7474..6b0b5e517e12 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -230,32 +230,20 @@ void handle_page_fault(struct pt_regs *regs)
return;
/*
- * Fault-in kernel-space virtual memory on-demand.
- * The 'reference' page table is init_mm.pgd.
+ * Fault-in kernel-space virtual memory on-demand, for 32-bit
+ * architectures. The 'reference' page table is init_mm.pgd.
*
* NOTE! We MUST NOT take any locks for this case. We may
* be in an interrupt or a critical region, and should
* only copy the information from the master page table,
* nothing more.
*/
- if (unlikely((addr >= VMALLOC_START) && (addr < VMALLOC_END))) {
+ if (!IS_ENABLED(CONFIG_64BIT) &&
+ unlikely(addr >= VMALLOC_START && addr < VMALLOC_END)) {
vmalloc_fault(regs, code, addr);
return;
}
-#ifdef CONFIG_64BIT
- /*
- * Modules in 64bit kernels lie in their own virtual region which is not
- * in the vmalloc region, but dealing with page faults in this region
- * or the vmalloc region amounts to doing the same thing: checking that
- * the mapping exists in init_mm.pgd and updating user page table, so
- * just use vmalloc_fault.
- */
- if (unlikely(addr >= MODULES_VADDR && addr < MODULES_END)) {
- vmalloc_fault(regs, code, addr);
- return;
- }
-#endif
/* Enable interrupts if they were enabled in the parent context. */
if (!regs_irqs_disabled(regs))
local_irq_enable();
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 747e5b1ef02d..38bd4dd95276 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1363,3 +1363,61 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
return vmemmap_populate_basepages(start, end, node, NULL);
}
#endif
+
+#ifdef CONFIG_64BIT
+/*
+ * Pre-allocates page-table pages for a specific area in the kernel
+ * page-table. Only the level which needs to be synchronized between
+ * all page-tables is allocated because the synchronization can be
+ * expensive.
+ */
+static void __init preallocate_pgd_pages_range(unsigned long start, unsigned long end,
+ const char *area)
+{
+ unsigned long addr;
+ const char *lvl;
+
+ for (addr = start; addr < end && addr >= start; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
+ pgd_t *pgd = pgd_offset_k(addr);
+ p4d_t *p4d;
+ pud_t *pud;
+ pmd_t *pmd;
+
+ lvl = "p4d";
+ p4d = p4d_alloc(&init_mm, pgd, addr);
+ if (!p4d)
+ goto failed;
+
+ if (pgtable_l5_enabled)
+ continue;
+
+ lvl = "pud";
+ pud = pud_alloc(&init_mm, p4d, addr);
+ if (!pud)
+ goto failed;
+
+ if (pgtable_l4_enabled)
+ continue;
+
+ lvl = "pmd";
+ pmd = pmd_alloc(&init_mm, pud, addr);
+ if (!pmd)
+ goto failed;
+ }
+ return;
+
+failed:
+ /*
+ * The pages have to be there now or they will be missing in
+ * process page-tables later.
+ */
+ panic("Failed to pre-allocate %s pages for %s area\n", lvl, area);
+}
+
+void __init pgtable_cache_init(void)
+{
+ preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc");
+ if (IS_ENABLED(CONFIG_MODULES))
+ preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
+}
+#endif
base-commit: ac9a78681b921877518763ba0e89202254349d1b
--
2.39.2
Björn Töpel <[email protected]> writes:
> From: Björn Töpel <[email protected]>
>
> The RISC-V port requires that kernel PGD entries are to be
> synchronized between MMs. This is done via the vmalloc_fault()
> function, that simply copies the PGD entries from init_mm to the
> faulting one.
>
> Historically, faulting in PGD entries have been a source for both bugs
> [1], and poor performance.
>
> One way to get rid of vmalloc faults is by pre-allocating the PGD
> entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on
> SV39). The pre-allocation function is pulled from Jörg Rödel's x86
> work, with the addition of 3-level page tables (PMD allocations).
>
> The pmd_alloc() function needs the ptlock cache to be initialized
> (when split page locks is enabled), so the pre-allocation is done in a
> RISC-V specific pgtable_cache_init() implementation.
>
> Pre-allocate the kernel PGD entries for the vmalloc/modules area, but
> only for 64b platforms.
>
> Link: https://lore.kernel.org/lkml/[email protected]/ # [1]
> Signed-off-by: Björn Töpel <[email protected]>
...and the build was bitten by nommu [1]. I'll hold off the v2 a bit, to
see if there's any other comments.
Björn
[1] https://patchwork.kernel.org/project/linux-riscv/patch/[email protected]/
Hi Bj?rn,
kernel test robot noticed the following build warnings:
[auto build test WARNING on ac9a78681b921877518763ba0e89202254349d1b]
url: https://github.com/intel-lab-lkp/linux/commits/Bj-rn-T-pel/riscv-mm-Pre-allocate-PGD-entries-vmalloc-modules-area/20230530-020212
base: ac9a78681b921877518763ba0e89202254349d1b
patch link: https://lore.kernel.org/r/20230529180023.289904-1-bjorn%40kernel.org
patch subject: [PATCH] riscv: mm: Pre-allocate PGD entries vmalloc/modules area
config: riscv-randconfig-r042-20230530 (https://download.01.org/0day-ci/archive/20230531/[email protected]/config)
compiler: riscv64-linux-gcc (GCC) 12.3.0
reproduce (this is a W=1 build):
mkdir -p ~/bin
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/9383adbcdfb7f850149742579615e8c174328a78
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Bj-rn-T-pel/riscv-mm-Pre-allocate-PGD-entries-vmalloc-modules-area/20230530-020212
git checkout 9383adbcdfb7f850149742579615e8c174328a78
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.3.0 ~/bin/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.3.0 ~/bin/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash arch/riscv/mm/
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
All warnings (new ones prefixed by >>):
arch/riscv/mm/init.c: In function 'preallocate_pgd_pages_range':
arch/riscv/mm/init.c:1381:30: error: implicit declaration of function 'pgd_offset_k'; did you mean 'p4d_offset'? [-Werror=implicit-function-declaration]
1381 | pgd_t *pgd = pgd_offset_k(addr);
| ^~~~~~~~~~~~
| p4d_offset
>> arch/riscv/mm/init.c:1381:30: warning: initialization of 'pgd_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
arch/riscv/mm/init.c:1387:23: error: implicit declaration of function 'p4d_alloc'; did you mean 'd_alloc'? [-Werror=implicit-function-declaration]
1387 | p4d = p4d_alloc(&init_mm, pgd, addr);
| ^~~~~~~~~
| d_alloc
>> arch/riscv/mm/init.c:1387:21: warning: assignment to 'p4d_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
1387 | p4d = p4d_alloc(&init_mm, pgd, addr);
| ^
arch/riscv/mm/init.c:1395:23: error: implicit declaration of function 'pud_alloc'; did you mean 'd_alloc'? [-Werror=implicit-function-declaration]
1395 | pud = pud_alloc(&init_mm, p4d, addr);
| ^~~~~~~~~
| d_alloc
>> arch/riscv/mm/init.c:1395:21: warning: assignment to 'pud_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
1395 | pud = pud_alloc(&init_mm, p4d, addr);
| ^
arch/riscv/mm/init.c:1403:23: error: implicit declaration of function 'pmd_alloc'; did you mean 'mm_alloc'? [-Werror=implicit-function-declaration]
1403 | pmd = pmd_alloc(&init_mm, pud, addr);
| ^~~~~~~~~
| mm_alloc
>> arch/riscv/mm/init.c:1403:21: warning: assignment to 'pmd_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
1403 | pmd = pmd_alloc(&init_mm, pud, addr);
| ^
arch/riscv/mm/init.c: In function 'pgtable_cache_init':
arch/riscv/mm/init.c:1421:45: error: 'MODULES_VADDR' undeclared (first use in this function)
1421 | preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
| ^~~~~~~~~~~~~
arch/riscv/mm/init.c:1421:45: note: each undeclared identifier is reported only once for each function it appears in
arch/riscv/mm/init.c:1421:60: error: 'MODULES_END' undeclared (first use in this function)
1421 | preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
| ^~~~~~~~~~~
cc1: some warnings being treated as errors
vim +1381 arch/riscv/mm/init.c
1366
1367 #ifdef CONFIG_64BIT
1368 /*
1369 * Pre-allocates page-table pages for a specific area in the kernel
1370 * page-table. Only the level which needs to be synchronized between
1371 * all page-tables is allocated because the synchronization can be
1372 * expensive.
1373 */
1374 static void __init preallocate_pgd_pages_range(unsigned long start, unsigned long end,
1375 const char *area)
1376 {
1377 unsigned long addr;
1378 const char *lvl;
1379
1380 for (addr = start; addr < end && addr >= start; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
> 1381 pgd_t *pgd = pgd_offset_k(addr);
1382 p4d_t *p4d;
1383 pud_t *pud;
1384 pmd_t *pmd;
1385
1386 lvl = "p4d";
> 1387 p4d = p4d_alloc(&init_mm, pgd, addr);
1388 if (!p4d)
1389 goto failed;
1390
1391 if (pgtable_l5_enabled)
1392 continue;
1393
1394 lvl = "pud";
> 1395 pud = pud_alloc(&init_mm, p4d, addr);
1396 if (!pud)
1397 goto failed;
1398
1399 if (pgtable_l4_enabled)
1400 continue;
1401
1402 lvl = "pmd";
> 1403 pmd = pmd_alloc(&init_mm, pud, addr);
1404 if (!pmd)
1405 goto failed;
1406 }
1407 return;
1408
1409 failed:
1410 /*
1411 * The pages have to be there now or they will be missing in
1412 * process page-tables later.
1413 */
1414 panic("Failed to pre-allocate %s pages for %s area\n", lvl, area);
1415 }
1416
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Hi Bj?rn,
kernel test robot noticed the following build errors:
[auto build test ERROR on ac9a78681b921877518763ba0e89202254349d1b]
url: https://github.com/intel-lab-lkp/linux/commits/Bj-rn-T-pel/riscv-mm-Pre-allocate-PGD-entries-vmalloc-modules-area/20230530-020212
base: ac9a78681b921877518763ba0e89202254349d1b
patch link: https://lore.kernel.org/r/20230529180023.289904-1-bjorn%40kernel.org
patch subject: [PATCH] riscv: mm: Pre-allocate PGD entries vmalloc/modules area
config: riscv-randconfig-r042-20230530 (https://download.01.org/0day-ci/archive/20230531/[email protected]/config)
compiler: riscv64-linux-gcc (GCC) 12.3.0
reproduce (this is a W=1 build):
mkdir -p ~/bin
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/9383adbcdfb7f850149742579615e8c174328a78
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Bj-rn-T-pel/riscv-mm-Pre-allocate-PGD-entries-vmalloc-modules-area/20230530-020212
git checkout 9383adbcdfb7f850149742579615e8c174328a78
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.3.0 ~/bin/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.3.0 ~/bin/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
All errors (new ones prefixed by >>):
arch/riscv/mm/init.c: In function 'preallocate_pgd_pages_range':
>> arch/riscv/mm/init.c:1381:30: error: implicit declaration of function 'pgd_offset_k'; did you mean 'p4d_offset'? [-Werror=implicit-function-declaration]
1381 | pgd_t *pgd = pgd_offset_k(addr);
| ^~~~~~~~~~~~
| p4d_offset
arch/riscv/mm/init.c:1381:30: warning: initialization of 'pgd_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
>> arch/riscv/mm/init.c:1387:23: error: implicit declaration of function 'p4d_alloc'; did you mean 'd_alloc'? [-Werror=implicit-function-declaration]
1387 | p4d = p4d_alloc(&init_mm, pgd, addr);
| ^~~~~~~~~
| d_alloc
arch/riscv/mm/init.c:1387:21: warning: assignment to 'p4d_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
1387 | p4d = p4d_alloc(&init_mm, pgd, addr);
| ^
>> arch/riscv/mm/init.c:1395:23: error: implicit declaration of function 'pud_alloc'; did you mean 'd_alloc'? [-Werror=implicit-function-declaration]
1395 | pud = pud_alloc(&init_mm, p4d, addr);
| ^~~~~~~~~
| d_alloc
arch/riscv/mm/init.c:1395:21: warning: assignment to 'pud_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
1395 | pud = pud_alloc(&init_mm, p4d, addr);
| ^
>> arch/riscv/mm/init.c:1403:23: error: implicit declaration of function 'pmd_alloc'; did you mean 'mm_alloc'? [-Werror=implicit-function-declaration]
1403 | pmd = pmd_alloc(&init_mm, pud, addr);
| ^~~~~~~~~
| mm_alloc
arch/riscv/mm/init.c:1403:21: warning: assignment to 'pmd_t *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
1403 | pmd = pmd_alloc(&init_mm, pud, addr);
| ^
arch/riscv/mm/init.c: In function 'pgtable_cache_init':
>> arch/riscv/mm/init.c:1421:45: error: 'MODULES_VADDR' undeclared (first use in this function)
1421 | preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
| ^~~~~~~~~~~~~
arch/riscv/mm/init.c:1421:45: note: each undeclared identifier is reported only once for each function it appears in
>> arch/riscv/mm/init.c:1421:60: error: 'MODULES_END' undeclared (first use in this function)
1421 | preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
| ^~~~~~~~~~~
cc1: some warnings being treated as errors
vim +1381 arch/riscv/mm/init.c
1366
1367 #ifdef CONFIG_64BIT
1368 /*
1369 * Pre-allocates page-table pages for a specific area in the kernel
1370 * page-table. Only the level which needs to be synchronized between
1371 * all page-tables is allocated because the synchronization can be
1372 * expensive.
1373 */
1374 static void __init preallocate_pgd_pages_range(unsigned long start, unsigned long end,
1375 const char *area)
1376 {
1377 unsigned long addr;
1378 const char *lvl;
1379
1380 for (addr = start; addr < end && addr >= start; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
> 1381 pgd_t *pgd = pgd_offset_k(addr);
1382 p4d_t *p4d;
1383 pud_t *pud;
1384 pmd_t *pmd;
1385
1386 lvl = "p4d";
> 1387 p4d = p4d_alloc(&init_mm, pgd, addr);
1388 if (!p4d)
1389 goto failed;
1390
1391 if (pgtable_l5_enabled)
1392 continue;
1393
1394 lvl = "pud";
> 1395 pud = pud_alloc(&init_mm, p4d, addr);
1396 if (!pud)
1397 goto failed;
1398
1399 if (pgtable_l4_enabled)
1400 continue;
1401
1402 lvl = "pmd";
> 1403 pmd = pmd_alloc(&init_mm, pud, addr);
1404 if (!pmd)
1405 goto failed;
1406 }
1407 return;
1408
1409 failed:
1410 /*
1411 * The pages have to be there now or they will be missing in
1412 * process page-tables later.
1413 */
1414 panic("Failed to pre-allocate %s pages for %s area\n", lvl, area);
1415 }
1416
1417 void __init pgtable_cache_init(void)
1418 {
1419 preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc");
1420 if (IS_ENABLED(CONFIG_MODULES))
> 1421 preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On Mon, 29 May 2023 11:00:23 PDT (-0700), [email protected] wrote:
> From: Björn Töpel <[email protected]>
>
> The RISC-V port requires that kernel PGD entries are to be
> synchronized between MMs. This is done via the vmalloc_fault()
> function, that simply copies the PGD entries from init_mm to the
> faulting one.
>
> Historically, faulting in PGD entries have been a source for both bugs
> [1], and poor performance.
>
> One way to get rid of vmalloc faults is by pre-allocating the PGD
> entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on
> SV39). The pre-allocation function is pulled from Jörg Rödel's x86
> work, with the addition of 3-level page tables (PMD allocations).
>
> The pmd_alloc() function needs the ptlock cache to be initialized
> (when split page locks is enabled), so the pre-allocation is done in a
> RISC-V specific pgtable_cache_init() implementation.
>
> Pre-allocate the kernel PGD entries for the vmalloc/modules area, but
> only for 64b platforms.
>
> Link: https://lore.kernel.org/lkml/[email protected]/ # [1]
> Signed-off-by: Björn Töpel <[email protected]>
> ---
> arch/riscv/mm/fault.c | 20 +++------------
> arch/riscv/mm/init.c | 58 +++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 62 insertions(+), 16 deletions(-)
>
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 8685f85a7474..6b0b5e517e12 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -230,32 +230,20 @@ void handle_page_fault(struct pt_regs *regs)
> return;
>
> /*
> - * Fault-in kernel-space virtual memory on-demand.
> - * The 'reference' page table is init_mm.pgd.
> + * Fault-in kernel-space virtual memory on-demand, for 32-bit
> + * architectures. The 'reference' page table is init_mm.pgd.
That wording seems a little odd to me: I think English allows for these
"add something after the comma to change the meaning of a sentence"
things, but they're kind of complicated. Maybe it's easier to just flip
the order?
That said, it's very early so maybe it's fine...
> *
> * NOTE! We MUST NOT take any locks for this case. We may
> * be in an interrupt or a critical region, and should
> * only copy the information from the master page table,
> * nothing more.
> */
> - if (unlikely((addr >= VMALLOC_START) && (addr < VMALLOC_END))) {
> + if (!IS_ENABLED(CONFIG_64BIT) &&
> + unlikely(addr >= VMALLOC_START && addr < VMALLOC_END)) {
> vmalloc_fault(regs, code, addr);
> return;
> }
>
> -#ifdef CONFIG_64BIT
> - /*
> - * Modules in 64bit kernels lie in their own virtual region which is not
> - * in the vmalloc region, but dealing with page faults in this region
> - * or the vmalloc region amounts to doing the same thing: checking that
> - * the mapping exists in init_mm.pgd and updating user page table, so
> - * just use vmalloc_fault.
> - */
> - if (unlikely(addr >= MODULES_VADDR && addr < MODULES_END)) {
> - vmalloc_fault(regs, code, addr);
> - return;
> - }
> -#endif
> /* Enable interrupts if they were enabled in the parent context. */
> if (!regs_irqs_disabled(regs))
> local_irq_enable();
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 747e5b1ef02d..38bd4dd95276 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -1363,3 +1363,61 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> return vmemmap_populate_basepages(start, end, node, NULL);
> }
> #endif
> +
> +#ifdef CONFIG_64BIT
> +/*
> + * Pre-allocates page-table pages for a specific area in the kernel
> + * page-table. Only the level which needs to be synchronized between
> + * all page-tables is allocated because the synchronization can be
> + * expensive.
> + */
> +static void __init preallocate_pgd_pages_range(unsigned long start, unsigned long end,
> + const char *area)
> +{
> + unsigned long addr;
> + const char *lvl;
> +
> + for (addr = start; addr < end && addr >= start; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
> + pgd_t *pgd = pgd_offset_k(addr);
> + p4d_t *p4d;
> + pud_t *pud;
> + pmd_t *pmd;
> +
> + lvl = "p4d";
> + p4d = p4d_alloc(&init_mm, pgd, addr);
> + if (!p4d)
> + goto failed;
> +
> + if (pgtable_l5_enabled)
> + continue;
> +
> + lvl = "pud";
> + pud = pud_alloc(&init_mm, p4d, addr);
> + if (!pud)
> + goto failed;
> +
> + if (pgtable_l4_enabled)
> + continue;
> +
> + lvl = "pmd";
> + pmd = pmd_alloc(&init_mm, pud, addr);
> + if (!pmd)
> + goto failed;
> + }
> + return;
> +
> +failed:
> + /*
> + * The pages have to be there now or they will be missing in
> + * process page-tables later.
> + */
> + panic("Failed to pre-allocate %s pages for %s area\n", lvl, area);
> +}
> +
> +void __init pgtable_cache_init(void)
> +{
> + preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc");
> + if (IS_ENABLED(CONFIG_MODULES))
> + preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
> +}
> +#endif
>
> base-commit: ac9a78681b921877518763ba0e89202254349d1b
Reviewed-by: Palmer Dabbelt <[email protected]>
aside from the build issue, which seems pretty straight-forward. I'm
going to drop this from patchwork.
Palmer Dabbelt <[email protected]> writes:
> On Mon, 29 May 2023 11:00:23 PDT (-0700), [email protected] wrote:
>> From: Björn Töpel <[email protected]>
>>
>> The RISC-V port requires that kernel PGD entries are to be
>> synchronized between MMs. This is done via the vmalloc_fault()
>> function, that simply copies the PGD entries from init_mm to the
>> faulting one.
>>
>> Historically, faulting in PGD entries have been a source for both bugs
>> [1], and poor performance.
>>
>> One way to get rid of vmalloc faults is by pre-allocating the PGD
>> entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on
>> SV39). The pre-allocation function is pulled from Jörg Rödel's x86
>> work, with the addition of 3-level page tables (PMD allocations).
>>
>> The pmd_alloc() function needs the ptlock cache to be initialized
>> (when split page locks is enabled), so the pre-allocation is done in a
>> RISC-V specific pgtable_cache_init() implementation.
>>
>> Pre-allocate the kernel PGD entries for the vmalloc/modules area, but
>> only for 64b platforms.
>>
>> Link: https://lore.kernel.org/lkml/[email protected]/ # [1]
>> Signed-off-by: Björn Töpel <[email protected]>
>> ---
>> arch/riscv/mm/fault.c | 20 +++------------
>> arch/riscv/mm/init.c | 58 +++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 62 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>> index 8685f85a7474..6b0b5e517e12 100644
>> --- a/arch/riscv/mm/fault.c
>> +++ b/arch/riscv/mm/fault.c
>> @@ -230,32 +230,20 @@ void handle_page_fault(struct pt_regs *regs)
>> return;
>>
>> /*
>> - * Fault-in kernel-space virtual memory on-demand.
>> - * The 'reference' page table is init_mm.pgd.
>> + * Fault-in kernel-space virtual memory on-demand, for 32-bit
>> + * architectures. The 'reference' page table is init_mm.pgd.
>
> That wording seems a little odd to me: I think English allows for these
> "add something after the comma to change the meaning of a sentence"
> things, but they're kind of complicated. Maybe it's easier to just flip
> the order?
>
> That said, it's very early so maybe it's fine...
>
>> *
>> * NOTE! We MUST NOT take any locks for this case. We may
>> * be in an interrupt or a critical region, and should
>> * only copy the information from the master page table,
>> * nothing more.
>> */
>> - if (unlikely((addr >= VMALLOC_START) && (addr < VMALLOC_END))) {
>> + if (!IS_ENABLED(CONFIG_64BIT) &&
>> + unlikely(addr >= VMALLOC_START && addr < VMALLOC_END)) {
>> vmalloc_fault(regs, code, addr);
>> return;
>> }
>>
>> -#ifdef CONFIG_64BIT
>> - /*
>> - * Modules in 64bit kernels lie in their own virtual region which is not
>> - * in the vmalloc region, but dealing with page faults in this region
>> - * or the vmalloc region amounts to doing the same thing: checking that
>> - * the mapping exists in init_mm.pgd and updating user page table, so
>> - * just use vmalloc_fault.
>> - */
>> - if (unlikely(addr >= MODULES_VADDR && addr < MODULES_END)) {
>> - vmalloc_fault(regs, code, addr);
>> - return;
>> - }
>> -#endif
>> /* Enable interrupts if they were enabled in the parent context. */
>> if (!regs_irqs_disabled(regs))
>> local_irq_enable();
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 747e5b1ef02d..38bd4dd95276 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -1363,3 +1363,61 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>> return vmemmap_populate_basepages(start, end, node, NULL);
>> }
>> #endif
>> +
>> +#ifdef CONFIG_64BIT
>> +/*
>> + * Pre-allocates page-table pages for a specific area in the kernel
>> + * page-table. Only the level which needs to be synchronized between
>> + * all page-tables is allocated because the synchronization can be
>> + * expensive.
>> + */
>> +static void __init preallocate_pgd_pages_range(unsigned long start, unsigned long end,
>> + const char *area)
>> +{
>> + unsigned long addr;
>> + const char *lvl;
>> +
>> + for (addr = start; addr < end && addr >= start; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
>> + pgd_t *pgd = pgd_offset_k(addr);
>> + p4d_t *p4d;
>> + pud_t *pud;
>> + pmd_t *pmd;
>> +
>> + lvl = "p4d";
>> + p4d = p4d_alloc(&init_mm, pgd, addr);
>> + if (!p4d)
>> + goto failed;
>> +
>> + if (pgtable_l5_enabled)
>> + continue;
>> +
>> + lvl = "pud";
>> + pud = pud_alloc(&init_mm, p4d, addr);
>> + if (!pud)
>> + goto failed;
>> +
>> + if (pgtable_l4_enabled)
>> + continue;
>> +
>> + lvl = "pmd";
>> + pmd = pmd_alloc(&init_mm, pud, addr);
>> + if (!pmd)
>> + goto failed;
>> + }
>> + return;
>> +
>> +failed:
>> + /*
>> + * The pages have to be there now or they will be missing in
>> + * process page-tables later.
>> + */
>> + panic("Failed to pre-allocate %s pages for %s area\n", lvl, area);
>> +}
>> +
>> +void __init pgtable_cache_init(void)
>> +{
>> + preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc");
>> + if (IS_ENABLED(CONFIG_MODULES))
>> + preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
>> +}
>> +#endif
>>
>> base-commit: ac9a78681b921877518763ba0e89202254349d1b
>
> Reviewed-by: Palmer Dabbelt <[email protected]>
>
> aside from the build issue, which seems pretty straight-forward. I'm
> going to drop this from patchwork.
Hmm, you applied the V2 a couple of days ago [1], which fixes the build
issue. Did you drop the V2 from the queue?
[1]
https://lore.kernel.org/linux-riscv/168727442024.569.16572247474971535604.git-patchwork-notify@kernel.org/
Björn