riscv: mm: Pre-allocate PGD entries vmalloc/modules area

Commit Message

Björn Töpel May 29, 2023, 6 p.m. UTC

From: Björn Töpel <[e-mail]>

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/[e-mail]/ # [1]
Signed-off-by: Björn Töpel <[e-mail]>
---
 arch/riscv/mm/fault.c | 20 +++------------
 arch/riscv/mm/init.c  | 58 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 16 deletions(-)


base-commit: ac9a78681b921877518763ba0e89202254349d1b

Comments

Björn Töpel May 30, 2023, 6:37 a.m. UTC | #1

Björn Töpel <[e-mail]> writes:

> From: Björn Töpel <[e-mail]>
>
> 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/[e-mail]/ # [1]
> Signed-off-by: Björn Töpel <[e-mail]>

...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/[e-mail]/

kernel test robot May 31, 2023, 12:32 a.m. UTC | #2

Hi Björn,

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/[e-mail]/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 <[e-mail]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/

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

kernel test robot May 31, 2023, 3:39 a.m. UTC | #3

Hi Björn,

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/[e-mail]/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 <[e-mail]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/

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");

Palmer Dabbelt June 22, 2023, 3:13 p.m. UTC | #4

On Mon, 29 May 2023 11:00:23 PDT (-0700), [e-mail] wrote:
> From: Björn Töpel <[e-mail]>
>
> 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/[e-mail]/ # [1]
> Signed-off-by: Björn Töpel <[e-mail]>
> ---
>  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 <[e-mail]>

aside from the build issue, which seems pretty straight-forward.  I'm 
going to drop this from patchwork.

Björn Töpel June 22, 2023, 3:51 p.m. UTC | #5

Palmer Dabbelt <[e-mail]> writes:

> On Mon, 29 May 2023 11:00:23 PDT (-0700), [e-mail] wrote:
>> From: Björn Töpel <[e-mail]>
>>
>> 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/[e-mail]/ # [1]
>> Signed-off-by: Björn Töpel <[e-mail]>
>> ---
>>  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 <[e-mail]>
>
> 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/[e-mail]/


Björn

Patch

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