RE: [RFC PATCH 0/2] Avoid booting stall caused by idmap_kpti_install_ng_mappings
Hi Marc
> -Original Message-
> From: Justin He
> Sent: Wednesday, January 20, 2021 11:56 PM
> To: Marc Zyngier
> Cc: Catalin Marinas ; Will Deacon
> ; linux-arm-ker...@lists.infradead.org; linux-
> ker...@vger.kernel.org; Anshuman Khandual ;
> Suzuki Poulose ; Mark Rutland
> ; Gustavo A. R. Silva ;
> Richard Henderson ; Dave P Martin
> ; Steven Price ; Andrew Morton
> ; Mike Rapoport ; Ard
> Biesheuvel ; Gavin Shan ; Kefeng Wang
> ; Mark Brown ; Cristian
> Marussi
> Subject: RE: [RFC PATCH 0/2] Avoid booting stall caused by
> idmap_kpti_install_ng_mappings
>
> Hi Marc
>
> > -Original Message-
> > From: Marc Zyngier
> > Sent: Wednesday, January 20, 2021 6:58 PM
> > To: Justin He
> > Cc: Catalin Marinas ; Will Deacon
> > ; linux-arm-ker...@lists.infradead.org; linux-
> > ker...@vger.kernel.org; Anshuman Khandual ;
> > Suzuki Poulose ; Mark Rutland
> > ; Gustavo A. R. Silva ;
> > Richard Henderson ; Dave P Martin
> > ; Steven Price ; Andrew Morton
> > ; Mike Rapoport ; Ard
> > Biesheuvel ; Gavin Shan ; Kefeng Wang
> > ; Mark Brown ; Cristian
> > Marussi
> > Subject: Re: [RFC PATCH 0/2] Avoid booting stall caused by
> > idmap_kpti_install_ng_mappings
> >
> > Hi Justin,
> >
> > On 2021-01-20 04:51, Justin He wrote:
> > > Hi,
> > > Kindly ping
> > >
> > >> -Original Message-
> > >> From: Jia He
> > >> Sent: Wednesday, January 13, 2021 9:41 AM
> > >> To: Catalin Marinas ; Will Deacon
> > >> ; linux-arm-ker...@lists.infradead.org; linux-
> > >> ker...@vger.kernel.org
> > >> Cc: Anshuman Khandual ; Suzuki Poulose
> > >> ; Justin He ; Mark Rutland
> > >> ; Gustavo A. R. Silva ;
> > >> Richard Henderson ; Dave P Martin
> > >> ; Steven Price ; Andrew
> > >> Morton
> > >> ; Mike Rapoport ; Ard
> > >> Biesheuvel ; Gavin Shan ; Kefeng
> > >> Wang
> > >> ; Mark Brown ; Marc
> > >> Zyngier
> > >> ; Cristian Marussi
> > >> Subject: [RFC PATCH 0/2] Avoid booting stall caused by
> > >>
> > >> There is a 10s stall in idmap_kpti_install_ng_mappings when kernel
> > >> boots
> > >> on a Ampere EMAG server.
> > >>
> > >> Commit f992b4dfd58b ("arm64: kpti: Add ->enable callback to remap
> > >> swapper using nG mappings") updates the nG bit runtime if kpti is
> > >> required.
> > >>
> > >> But things get worse if rodata=full in map_mem(). NO_BLOCK_MAPPINGS |
> > >> NO_CONT_MAPPINGS is required when creating pagetable mapping. Hence
> > >> all
> > >> ptes are fully mapped in this case. On a Ampere EMAG server with 256G
> > >> memory(pagesize=4k), it causes the 10s stall.
> > >>
> > >> After moving init_cpu_features() ahead of early_fixmap_init(), we can
> > >> use
> > >> cpu_have_const_cap earlier than before. Hence we can avoid this stall
> > >> by updating arm64_use_ng_mappings.
> > >>
> > >> After this patch series, it reduces the kernel boot time from 14.7s to
> > >> 4.1s:
> > >> Before:
> > >> [ 14.757569] Freeing initrd memory: 60752K
> > >> After:
> > >> [4.138819] Freeing initrd memory: 60752K
> > >>
> > >> Set it as RFC because I want to resolve any other points which I have
> > >> misconerned.
> >
> > But you don't really explain *why* having the CPU Feature discovery
> > early helps at all. Is that so that you can bypass the idmap mapping?
>
> Adding nG bits can be avoided by having the discovery of boot cpu feature
> earlier since the nG bit had been set in PTE_MAYBE_NG/PMD_MAYBE_NG
>
> Before this patch:
> 1. kernel will firstly create mapping in setup_arch->paging_init->map_mem
> -> __map_memblock
> 2. Then if kpti is required, kernel will add nG bits for each pte entry.
> 3. In extreme case, e.g. physical memory is 256G,rodata=full, and pagesize
> is 4K, the nG bits updating in step 2 takes about 10s.
>
> > I'd expect something that explain the problem instead of paraphrasing
> > the patches.
> >
> > Another thing is whether you have tested this on some ThunderX HW
>
> I will find a TX1 as you told to see any difference.
>
>
I fortunately found a cavium TX1.
Seems that unmap_kernel_at_el0 is false:
...
[0.00] Machine model: Cavium ThunderX CN88XX board
...
[0.00] CPU features: kernel page table isolation forced OFF by
ARM64_WORKAROUND_CAVIUM_27456
...
Hence no such stall *before* and *after* this patch set because kpti is not
enabled.
--
Cheers,
Justin (Jia He)
RE: [RFC PATCH 0/2] Avoid booting stall caused by idmap_kpti_install_ng_mappings
Hi Marc
> -Original Message-
> From: Marc Zyngier
> Sent: Wednesday, January 20, 2021 6:58 PM
> To: Justin He
> Cc: Catalin Marinas ; Will Deacon
> ; linux-arm-ker...@lists.infradead.org; linux-
> ker...@vger.kernel.org; Anshuman Khandual ;
> Suzuki Poulose ; Mark Rutland
> ; Gustavo A. R. Silva ;
> Richard Henderson ; Dave P Martin
> ; Steven Price ; Andrew Morton
> ; Mike Rapoport ; Ard
> Biesheuvel ; Gavin Shan ; Kefeng Wang
> ; Mark Brown ; Cristian
> Marussi
> Subject: Re: [RFC PATCH 0/2] Avoid booting stall caused by
> idmap_kpti_install_ng_mappings
>
> Hi Justin,
>
> On 2021-01-20 04:51, Justin He wrote:
> > Hi,
> > Kindly ping
> >
> >> -Original Message-
> >> From: Jia He
> >> Sent: Wednesday, January 13, 2021 9:41 AM
> >> To: Catalin Marinas ; Will Deacon
> >> ; linux-arm-ker...@lists.infradead.org; linux-
> >> ker...@vger.kernel.org
> >> Cc: Anshuman Khandual ; Suzuki Poulose
> >> ; Justin He ; Mark Rutland
> >> ; Gustavo A. R. Silva ;
> >> Richard Henderson ; Dave P Martin
> >> ; Steven Price ; Andrew
> >> Morton
> >> ; Mike Rapoport ; Ard
> >> Biesheuvel ; Gavin Shan ; Kefeng
> >> Wang
> >> ; Mark Brown ; Marc
> >> Zyngier
> >> ; Cristian Marussi
> >> Subject: [RFC PATCH 0/2] Avoid booting stall caused by
> >>
> >> There is a 10s stall in idmap_kpti_install_ng_mappings when kernel
> >> boots
> >> on a Ampere EMAG server.
> >>
> >> Commit f992b4dfd58b ("arm64: kpti: Add ->enable callback to remap
> >> swapper using nG mappings") updates the nG bit runtime if kpti is
> >> required.
> >>
> >> But things get worse if rodata=full in map_mem(). NO_BLOCK_MAPPINGS |
> >> NO_CONT_MAPPINGS is required when creating pagetable mapping. Hence
> >> all
> >> ptes are fully mapped in this case. On a Ampere EMAG server with 256G
> >> memory(pagesize=4k), it causes the 10s stall.
> >>
> >> After moving init_cpu_features() ahead of early_fixmap_init(), we can
> >> use
> >> cpu_have_const_cap earlier than before. Hence we can avoid this stall
> >> by updating arm64_use_ng_mappings.
> >>
> >> After this patch series, it reduces the kernel boot time from 14.7s to
> >> 4.1s:
> >> Before:
> >> [ 14.757569] Freeing initrd memory: 60752K
> >> After:
> >> [4.138819] Freeing initrd memory: 60752K
> >>
> >> Set it as RFC because I want to resolve any other points which I have
> >> misconerned.
>
> But you don't really explain *why* having the CPU Feature discovery
> early helps at all. Is that so that you can bypass the idmap mapping?
Adding nG bits can be avoided by having the discovery of boot cpu feature
earlier since the nG bit had been set in PTE_MAYBE_NG/PMD_MAYBE_NG
Before this patch:
1. kernel will firstly create mapping in setup_arch->paging_init->map_mem
-> __map_memblock
2. Then if kpti is required, kernel will add nG bits for each pte entry.
3. In extreme case, e.g. physical memory is 256G,rodata=full, and pagesize
is 4K, the nG bits updating in step 2 takes about 10s.
> I'd expect something that explain the problem instead of paraphrasing
> the patches.
>
> Another thing is whether you have tested this on some ThunderX HW
I will find a TX1 as you told to see any difference.
--
Cheers,
Justin (Jia He)
> (the first version, not TX2), as this is the whole reason for this
> code...
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...
Re: [RFC PATCH 0/2] Avoid booting stall caused by idmap_kpti_install_ng_mappings
Hi Justin,
On 2021-01-20 04:51, Justin He wrote:
Hi,
Kindly ping
-Original Message-
From: Jia He
Sent: Wednesday, January 13, 2021 9:41 AM
To: Catalin Marinas ; Will Deacon
; linux-arm-ker...@lists.infradead.org; linux-
ker...@vger.kernel.org
Cc: Anshuman Khandual ; Suzuki Poulose
; Justin He ; Mark Rutland
; Gustavo A. R. Silva ;
Richard Henderson ; Dave P Martin
; Steven Price ; Andrew
Morton
; Mike Rapoport ; Ard
Biesheuvel ; Gavin Shan ; Kefeng
Wang
; Mark Brown ; Marc
Zyngier
; Cristian Marussi
Subject: [RFC PATCH 0/2] Avoid booting stall caused by
There is a 10s stall in idmap_kpti_install_ng_mappings when kernel
boots
on a Ampere EMAG server.
Commit f992b4dfd58b ("arm64: kpti: Add ->enable callback to remap
swapper using nG mappings") updates the nG bit runtime if kpti is
required.
But things get worse if rodata=full in map_mem(). NO_BLOCK_MAPPINGS |
NO_CONT_MAPPINGS is required when creating pagetable mapping. Hence
all
ptes are fully mapped in this case. On a Ampere EMAG server with 256G
memory(pagesize=4k), it causes the 10s stall.
After moving init_cpu_features() ahead of early_fixmap_init(), we can
use
cpu_have_const_cap earlier than before. Hence we can avoid this stall
by updating arm64_use_ng_mappings.
After this patch series, it reduces the kernel boot time from 14.7s to
4.1s:
Before:
[ 14.757569] Freeing initrd memory: 60752K
After:
[4.138819] Freeing initrd memory: 60752K
Set it as RFC because I want to resolve any other points which I have
misconerned.
But you don't really explain *why* having the CPU Feature discovery
early helps at all. Is that so that you can bypass the idmap mapping?
I'd expect something that explain the problem instead of paraphrasing
the patches.
Another thing is whether you have tested this on some ThunderX HW
(the first version, not TX2), as this is the whole reason for this
code...
Thanks,
M.
--
Jazz is not dead. It just smells funny...
RE: [RFC PATCH 0/2] Avoid booting stall caused by idmap_kpti_install_ng_mappings
Hi,
Kindly ping
> -Original Message-
> From: Jia He
> Sent: Wednesday, January 13, 2021 9:41 AM
> To: Catalin Marinas ; Will Deacon
> ; linux-arm-ker...@lists.infradead.org; linux-
> ker...@vger.kernel.org
> Cc: Anshuman Khandual ; Suzuki Poulose
> ; Justin He ; Mark Rutland
> ; Gustavo A. R. Silva ;
> Richard Henderson ; Dave P Martin
> ; Steven Price ; Andrew Morton
> ; Mike Rapoport ; Ard
> Biesheuvel ; Gavin Shan ; Kefeng Wang
> ; Mark Brown ; Marc Zyngier
> ; Cristian Marussi
> Subject: [RFC PATCH 0/2] Avoid booting stall caused by
>
> There is a 10s stall in idmap_kpti_install_ng_mappings when kernel boots
> on a Ampere EMAG server.
>
> Commit f992b4dfd58b ("arm64: kpti: Add ->enable callback to remap
> swapper using nG mappings") updates the nG bit runtime if kpti is
> required.
>
> But things get worse if rodata=full in map_mem(). NO_BLOCK_MAPPINGS |
> NO_CONT_MAPPINGS is required when creating pagetable mapping. Hence all
> ptes are fully mapped in this case. On a Ampere EMAG server with 256G
> memory(pagesize=4k), it causes the 10s stall.
>
> After moving init_cpu_features() ahead of early_fixmap_init(), we can use
> cpu_have_const_cap earlier than before. Hence we can avoid this stall
> by updating arm64_use_ng_mappings.
>
> After this patch series, it reduces the kernel boot time from 14.7s to
> 4.1s:
> Before:
> [ 14.757569] Freeing initrd memory: 60752K
> After:
> [4.138819] Freeing initrd memory: 60752K
>
> Set it as RFC because I want to resolve any other points which I have
> misconerned.
>
> Jia He (2):
> arm64/cpuinfo: Move init_cpu_features() ahead of early_fixmap_init()
> arm64: kpti: Update arm64_use_ng_mappings before pagetable mapping
>
> arch/arm64/include/asm/cpu.h | 1 +
> arch/arm64/kernel/cpuinfo.c | 13 ++---
> arch/arm64/kernel/setup.c| 18 +-
> arch/arm64/kernel/smp.c | 3 +--
> 4 files changed, 25 insertions(+), 10 deletions(-)
>
> --
> 2.17.1
[RFC PATCH 0/2] Avoid booting stall caused by
There is a 10s stall in idmap_kpti_install_ng_mappings when kernel boots
on a Ampere EMAG server.
Commit f992b4dfd58b ("arm64: kpti: Add ->enable callback to remap
swapper using nG mappings") updates the nG bit runtime if kpti is
required.
But things get worse if rodata=full in map_mem(). NO_BLOCK_MAPPINGS |
NO_CONT_MAPPINGS is required when creating pagetable mapping. Hence all
ptes are fully mapped in this case. On a Ampere EMAG server with 256G
memory(pagesize=4k), it causes the 10s stall.
After moving init_cpu_features() ahead of early_fixmap_init(), we can use
cpu_have_const_cap earlier than before. Hence we can avoid this stall
by updating arm64_use_ng_mappings.
After this patch series, it reduces the kernel boot time from 14.7s to
4.1s:
Before:
[ 14.757569] Freeing initrd memory: 60752K
After:
[4.138819] Freeing initrd memory: 60752K
Set it as RFC because I want to resolve any other points which I have
misconerned.
Jia He (2):
arm64/cpuinfo: Move init_cpu_features() ahead of early_fixmap_init()
arm64: kpti: Update arm64_use_ng_mappings before pagetable mapping
arch/arm64/include/asm/cpu.h | 1 +
arch/arm64/kernel/cpuinfo.c | 13 ++---
arch/arm64/kernel/setup.c| 18 +-
arch/arm64/kernel/smp.c | 3 +--
4 files changed, 25 insertions(+), 10 deletions(-)
--
2.17.1
