| Message ID | 20200225073731.465270-4-avagin@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: add the time namespace support | expand |
On 2/25/20 7:37 AM, Andrei Vagin wrote: > Allocate the time namespace page among VVAR pages. Provide > __arch_get_timens_vdso_data() helper for VDSO code to get the > code-relative position of VVARs on that special page. > > If a task belongs to a time namespace then the VVAR page which contains > the system wide VDSO data is replaced with a namespace specific page > which has the same layout as the VVAR page. That page has vdso_data->seq > set to 1 to enforce the slow path and vdso_data->clock_mode set to > VCLOCK_TIMENS to enforce the time namespace handling path. > > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent > update of the VDSO data is in progress, is not really affecting regular > tasks which are not part of a time namespace as the task is spin waiting > for the update to finish and vdso_data->seq to become even again. > > If a time namespace task hits that code path, it invokes the corresponding > time getter function which retrieves the real VVAR page, reads host time > and then adds the offset for the requested clock which is stored in the > special VVAR page. > > Signed-off-by: Andrei Vagin <avagin@gmail.com> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > --- > arch/arm64/include/asm/vdso.h | 6 ++++++ > .../include/asm/vdso/compat_gettimeofday.h | 11 ++++++++++ > arch/arm64/include/asm/vdso/gettimeofday.h | 8 ++++++++ > arch/arm64/kernel/vdso.c | 20 ++++++++++++++++--- > arch/arm64/kernel/vdso/vdso.lds.S | 5 ++++- > arch/arm64/kernel/vdso32/vdso.lds.S | 5 ++++- > include/vdso/datapage.h | 1 + > 7 files changed, 51 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h > index 07468428fd29..351c145d3808 100644 > --- a/arch/arm64/include/asm/vdso.h > +++ b/arch/arm64/include/asm/vdso.h > @@ -12,6 +12,12 @@ > */ > #define VDSO_LBASE 0x0 > > +#ifdef CONFIG_TIME_NS > +#define __VVAR_PAGES 2 > +#else > +#define __VVAR_PAGES 1 > +#endif > + > #ifndef __ASSEMBLY__ > > #include <generated/vdso-offsets.h> > diff --git a/arch/arm64/include/asm/vdso/compat_gettimeofday.h b/arch/arm64/include/asm/vdso/compat_gettimeofday.h > index 81b0c394f1d8..042814339a63 100644 > --- a/arch/arm64/include/asm/vdso/compat_gettimeofday.h > +++ b/arch/arm64/include/asm/vdso/compat_gettimeofday.h > @@ -160,6 +160,17 @@ static __always_inline const struct vdso_data *__arch_get_vdso_data(void) > return ret; > } > > +#ifdef CONFIG_TIME_NS > +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void) > +{ > + const struct vdso_data *ret; > + > + asm volatile("mov %0, %1" : "=r"(ret) : "r"(_timens_data)); > + > + return ret; > +} > +#endif > + > #endif /* !__ASSEMBLY__ */ > > #endif /* __ASM_VDSO_GETTIMEOFDAY_H */ > diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h > index 5a534432aa5d..553bdc19a91f 100644 > --- a/arch/arm64/include/asm/vdso/gettimeofday.h > +++ b/arch/arm64/include/asm/vdso/gettimeofday.h > @@ -97,6 +97,14 @@ const struct vdso_data *__arch_get_vdso_data(void) > return _vdso_data; > } > > +#ifdef CONFIG_TIME_NS > +static __always_inline > +const struct vdso_data *__arch_get_timens_vdso_data(void) > +{ > + return _timens_data; > +} > +#endif > + > #endif /* !__ASSEMBLY__ */ > > #endif /* __ASM_VDSO_GETTIMEOFDAY_H */ > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > index 6ac9cdeac5be..b3e7ce24e59b 100644 > --- a/arch/arm64/kernel/vdso.c > +++ b/arch/arm64/kernel/vdso.c > @@ -46,6 +46,14 @@ enum arch_vdso_type { > #define VDSO_TYPES (ARM64_VDSO + 1) > #endif /* CONFIG_COMPAT_VDSO */ > > +enum vvar_pages { > + VVAR_DATA_PAGE_OFFSET = 0, > +#ifdef CONFIG_TIME_NS > + VVAR_TIMENS_PAGE_OFFSET = 1, > +#endif /* CONFIG_TIME_NS */ > + VVAR_NR_PAGES = __VVAR_PAGES, > +}; > + > struct __vdso_abi { > const char *name; > const char *vdso_code_start; > @@ -81,6 +89,12 @@ static union { > } vdso_data_store __page_aligned_data; > struct vdso_data *vdso_data = vdso_data_store.data; > > + > +struct vdso_data *arch_get_vdso_data(void *vvar_page) > +{ > + return (struct vdso_data *)(vvar_page); > +} > + > static int __vdso_remap(enum arch_vdso_type arch_index, > const struct vm_special_mapping *sm, > struct vm_area_struct *new_vma) > @@ -182,7 +196,7 @@ static int __setup_additional_pages(enum arch_vdso_type arch_index, > > vdso_text_len = vdso_lookup[arch_index].vdso_pages << PAGE_SHIFT; > /* Be sure to map the data page */ > - vdso_mapping_len = vdso_text_len + PAGE_SIZE; > + vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE; > > vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0); > if (IS_ERR_VALUE(vdso_base)) { > @@ -190,13 +204,13 @@ static int __setup_additional_pages(enum arch_vdso_type arch_index, > goto up_fail; > } > > - ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE, > + ret = _install_special_mapping(mm, vdso_base, VVAR_NR_PAGES * PAGE_SIZE, > VM_READ|VM_MAYREAD|VM_PFNMAP, > vdso_lookup[arch_index].dm); > if (IS_ERR(ret)) > goto up_fail; > > - vdso_base += PAGE_SIZE; > + vdso_base += VVAR_NR_PAGES * PAGE_SIZE; > mm->context.vdso = (void *)vdso_base; > ret = _install_special_mapping(mm, vdso_base, vdso_text_len, > VM_READ|VM_EXEC| > diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S > index 7ad2d3a0cd48..d808ad31e01f 100644 > --- a/arch/arm64/kernel/vdso/vdso.lds.S > +++ b/arch/arm64/kernel/vdso/vdso.lds.S > @@ -17,7 +17,10 @@ OUTPUT_ARCH(aarch64) > > SECTIONS > { > - PROVIDE(_vdso_data = . - PAGE_SIZE); > + PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE); > +#ifdef CONFIG_TIME_NS > + PROVIDE(_timens_data = _vdso_data + PAGE_SIZE); > +#endif > . = VDSO_LBASE + SIZEOF_HEADERS; > > .hash : { *(.hash) } :text > diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S > index a3944927eaeb..06cc60a9630f 100644 > --- a/arch/arm64/kernel/vdso32/vdso.lds.S > +++ b/arch/arm64/kernel/vdso32/vdso.lds.S > @@ -17,7 +17,10 @@ OUTPUT_ARCH(arm) > > SECTIONS > { > - PROVIDE_HIDDEN(_vdso_data = . - PAGE_SIZE); > + PROVIDE_HIDDEN(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE); > +#ifdef CONFIG_TIME_NS > + PROVIDE_HIDDEN(_timens_data = _vdso_data + PAGE_SIZE); > +#endif > . = VDSO_LBASE + SIZEOF_HEADERS; > > .hash : { *(.hash) } :text > diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h > index 30c4cb0428d1..3494b5536b63 100644 > --- a/include/vdso/datapage.h > +++ b/include/vdso/datapage.h > @@ -98,6 +98,7 @@ struct vdso_data { > * relocation, and this is what we need. > */ > extern struct vdso_data _vdso_data[CS_BASES] __attribute__((visibility("hidden"))); > +extern struct vdso_data _timens_data[CS_BASES] __attribute__((visibility("hidden"))); > > #endif /* !__ASSEMBLY__ */ > >
On Mon, Feb 24, 2020 at 11:37:28PM -0800, Andrei Vagin wrote: > Allocate the time namespace page among VVAR pages. Provide > __arch_get_timens_vdso_data() helper for VDSO code to get the > code-relative position of VVARs on that special page. > > If a task belongs to a time namespace then the VVAR page which contains > the system wide VDSO data is replaced with a namespace specific page > which has the same layout as the VVAR page. That page has vdso_data->seq > set to 1 to enforce the slow path and vdso_data->clock_mode set to > VCLOCK_TIMENS to enforce the time namespace handling path. > > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent > update of the VDSO data is in progress, is not really affecting regular > tasks which are not part of a time namespace as the task is spin waiting > for the update to finish and vdso_data->seq to become even again. > > If a time namespace task hits that code path, it invokes the corresponding > time getter function which retrieves the real VVAR page, reads host time > and then adds the offset for the requested clock which is stored in the > special VVAR page. > > Signed-off-by: Andrei Vagin <avagin@gmail.com> > --- > arch/arm64/include/asm/vdso.h | 6 ++++++ > .../include/asm/vdso/compat_gettimeofday.h | 11 ++++++++++ > arch/arm64/include/asm/vdso/gettimeofday.h | 8 ++++++++ > arch/arm64/kernel/vdso.c | 20 ++++++++++++++++--- > arch/arm64/kernel/vdso/vdso.lds.S | 5 ++++- > arch/arm64/kernel/vdso32/vdso.lds.S | 5 ++++- > include/vdso/datapage.h | 1 + > 7 files changed, 51 insertions(+), 5 deletions(-) > +#ifdef CONFIG_TIME_NS > +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void) > +{ > + const struct vdso_data *ret; > + > + asm volatile("mov %0, %1" : "=r"(ret) : "r"(_timens_data)); > + > + return ret; > +} > +#endif What is this inline assembly for? The commit message doesn't mention it, there's no explanation here, and the native version doesn't do likewise so it seems rather surprising. Thanks, Mark. > diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h > index 5a534432aa5d..553bdc19a91f 100644 > --- a/arch/arm64/include/asm/vdso/gettimeofday.h > +++ b/arch/arm64/include/asm/vdso/gettimeofday.h > @@ -97,6 +97,14 @@ const struct vdso_data *__arch_get_vdso_data(void) > return _vdso_data; > } > > +#ifdef CONFIG_TIME_NS > +static __always_inline > +const struct vdso_data *__arch_get_timens_vdso_data(void) > +{ > + return _timens_data; > +} > +#endif
On Tue, Apr 14, 2020 at 10:20 AM Mark Rutland <mark.rutland@arm.com> wrote: > > On Mon, Feb 24, 2020 at 11:37:28PM -0800, Andrei Vagin wrote: > > Allocate the time namespace page among VVAR pages. Provide > > __arch_get_timens_vdso_data() helper for VDSO code to get the > > code-relative position of VVARs on that special page. > > > > If a task belongs to a time namespace then the VVAR page which contains > > the system wide VDSO data is replaced with a namespace specific page > > which has the same layout as the VVAR page. That page has vdso_data->seq > > set to 1 to enforce the slow path and vdso_data->clock_mode set to > > VCLOCK_TIMENS to enforce the time namespace handling path. > > > > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent > > update of the VDSO data is in progress, is not really affecting regular > > tasks which are not part of a time namespace as the task is spin waiting > > for the update to finish and vdso_data->seq to become even again. > > > > If a time namespace task hits that code path, it invokes the corresponding > > time getter function which retrieves the real VVAR page, reads host time > > and then adds the offset for the requested clock which is stored in the > > special VVAR page. > > > > Signed-off-by: Andrei Vagin <avagin@gmail.com> > > --- > > arch/arm64/include/asm/vdso.h | 6 ++++++ > > .../include/asm/vdso/compat_gettimeofday.h | 11 ++++++++++ > > arch/arm64/include/asm/vdso/gettimeofday.h | 8 ++++++++ > > arch/arm64/kernel/vdso.c | 20 ++++++++++++++++--- > > arch/arm64/kernel/vdso/vdso.lds.S | 5 ++++- > > arch/arm64/kernel/vdso32/vdso.lds.S | 5 ++++- > > include/vdso/datapage.h | 1 + > > 7 files changed, 51 insertions(+), 5 deletions(-) > > > +#ifdef CONFIG_TIME_NS > > +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void) > > +{ > > + const struct vdso_data *ret; > > + > > + asm volatile("mov %0, %1" : "=r"(ret) : "r"(_timens_data)); > > + > > + return ret; > > +} > > +#endif > > What is this inline assembly for? The commit message doesn't mention it, > there's no explanation here, and the native version doesn't do likewise > so it seems rather surprising. __arch_get_vdso_data is right before this function and there is a comment which explains this: https://github.com/torvalds/linux/blob/master/arch/arm64/include/asm/vdso/compat_gettimeofday.h#L137 """ /* * This simply puts &_vdso_data into ret. The reason why we don't use * `ret = _vdso_data` is that the compiler tends to optimize this in a * very suboptimal way: instead of keeping &_vdso_data in a register, * it goes through a relocation almost every time _vdso_data must be * accessed (even in subfunctions). This is both time and space * consuming: each relocation uses a word in the code section, and it * has to be loaded at runtime. * * This trick hides the assignment from the compiler. Since it cannot * track where the pointer comes from, it will only use one relocation * where __arch_get_vdso_data() is called, and then keep the result in * a register. */ """ I decided to not duplicate the comment because these two functions are very similar and close to each other. Thanks, Andrei
On Tue, Apr 14, 2020 at 07:34:41PM -0700, Andrei Vagin wrote: > On Tue, Apr 14, 2020 at 10:20 AM Mark Rutland <mark.rutland@arm.com> wrote: > > > > On Mon, Feb 24, 2020 at 11:37:28PM -0800, Andrei Vagin wrote: > > > Allocate the time namespace page among VVAR pages. Provide > > > __arch_get_timens_vdso_data() helper for VDSO code to get the > > > code-relative position of VVARs on that special page. > > > > > > If a task belongs to a time namespace then the VVAR page which contains > > > the system wide VDSO data is replaced with a namespace specific page > > > which has the same layout as the VVAR page. That page has vdso_data->seq > > > set to 1 to enforce the slow path and vdso_data->clock_mode set to > > > VCLOCK_TIMENS to enforce the time namespace handling path. > > > > > > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent > > > update of the VDSO data is in progress, is not really affecting regular > > > tasks which are not part of a time namespace as the task is spin waiting > > > for the update to finish and vdso_data->seq to become even again. > > > > > > If a time namespace task hits that code path, it invokes the corresponding > > > time getter function which retrieves the real VVAR page, reads host time > > > and then adds the offset for the requested clock which is stored in the > > > special VVAR page. > > > > > > Signed-off-by: Andrei Vagin <avagin@gmail.com> > > > --- > > > arch/arm64/include/asm/vdso.h | 6 ++++++ > > > .../include/asm/vdso/compat_gettimeofday.h | 11 ++++++++++ > > > arch/arm64/include/asm/vdso/gettimeofday.h | 8 ++++++++ > > > arch/arm64/kernel/vdso.c | 20 ++++++++++++++++--- > > > arch/arm64/kernel/vdso/vdso.lds.S | 5 ++++- > > > arch/arm64/kernel/vdso32/vdso.lds.S | 5 ++++- > > > include/vdso/datapage.h | 1 + > > > 7 files changed, 51 insertions(+), 5 deletions(-) > > > > > +#ifdef CONFIG_TIME_NS > > > +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void) > > > +{ > > > + const struct vdso_data *ret; > > > + > > > + asm volatile("mov %0, %1" : "=r"(ret) : "r"(_timens_data)); > > > + > > > + return ret; > > > +} > > > +#endif > > > > What is this inline assembly for? The commit message doesn't mention it, > > there's no explanation here, and the native version doesn't do likewise > > so it seems rather surprising. > > __arch_get_vdso_data is right before this function and there is a > comment which explains this: > https://github.com/torvalds/linux/blob/master/arch/arm64/include/asm/vdso/compat_gettimeofday.h#L137 > > """ > /* > * This simply puts &_vdso_data into ret. The reason why we don't use > * `ret = _vdso_data` is that the compiler tends to optimize this in a > * very suboptimal way: instead of keeping &_vdso_data in a register, > * it goes through a relocation almost every time _vdso_data must be > * accessed (even in subfunctions). This is both time and space > * consuming: each relocation uses a word in the code section, and it > * has to be loaded at runtime. > * > * This trick hides the assignment from the compiler. Since it cannot > * track where the pointer comes from, it will only use one relocation > * where __arch_get_vdso_data() is called, and then keep the result in > * a register. > */ > """ > > I decided to not duplicate the comment because these two functions are > very similar and close to each other. Ah, I was not aware of that context. Could we just add a trivial comment to say "see __arch_get_vdso_data" or something like that? It's a shame we're not using OPTIMIZER_HIDE_VAR() for that, as it can generate slightly better code and is easier to read than bare asm. Thanks, Mark.
Hi Mark, On 4/15/20 11:05 AM, Mark Rutland wrote: > It's a shame we're not using OPTIMIZER_HIDE_VAR() for that, as it can > generate slightly better code and is easier to read than bare asm. We are not because I was not aware when I wrote this code that such a macro existed :) But you are right it clearly makes the code more readable. To make up for it, I am happy to make the effort to introduce it for both the cases and replace the assembler once this patch series gets merged.
On Wed, Apr 15, 2020 at 11:16:00AM +0100, Vincenzo Frascino wrote: > Hi Mark, > > On 4/15/20 11:05 AM, Mark Rutland wrote: > > It's a shame we're not using OPTIMIZER_HIDE_VAR() for that, as it can > > generate slightly better code and is easier to read than bare asm. > > We are not because I was not aware when I wrote this code that such a macro > existed :) > > But you are right it clearly makes the code more readable. To make up for it, I > am happy to make the effort to introduce it for both the cases and replace the > assembler once this patch series gets merged. Sounds good to me! Mark.
diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h index 07468428fd29..351c145d3808 100644 --- a/arch/arm64/include/asm/vdso.h +++ b/arch/arm64/include/asm/vdso.h @@ -12,6 +12,12 @@ */ #define VDSO_LBASE 0x0 +#ifdef CONFIG_TIME_NS +#define __VVAR_PAGES 2 +#else +#define __VVAR_PAGES 1 +#endif + #ifndef __ASSEMBLY__ #include <generated/vdso-offsets.h> diff --git a/arch/arm64/include/asm/vdso/compat_gettimeofday.h b/arch/arm64/include/asm/vdso/compat_gettimeofday.h index 81b0c394f1d8..042814339a63 100644 --- a/arch/arm64/include/asm/vdso/compat_gettimeofday.h +++ b/arch/arm64/include/asm/vdso/compat_gettimeofday.h @@ -160,6 +160,17 @@ static __always_inline const struct vdso_data *__arch_get_vdso_data(void) return ret; } +#ifdef CONFIG_TIME_NS +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void) +{ + const struct vdso_data *ret; + + asm volatile("mov %0, %1" : "=r"(ret) : "r"(_timens_data)); + + return ret; +} +#endif + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_VDSO_GETTIMEOFDAY_H */ diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h index 5a534432aa5d..553bdc19a91f 100644 --- a/arch/arm64/include/asm/vdso/gettimeofday.h +++ b/arch/arm64/include/asm/vdso/gettimeofday.h @@ -97,6 +97,14 @@ const struct vdso_data *__arch_get_vdso_data(void) return _vdso_data; } +#ifdef CONFIG_TIME_NS +static __always_inline +const struct vdso_data *__arch_get_timens_vdso_data(void) +{ + return _timens_data; +} +#endif + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_VDSO_GETTIMEOFDAY_H */ diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c index 6ac9cdeac5be..b3e7ce24e59b 100644 --- a/arch/arm64/kernel/vdso.c +++ b/arch/arm64/kernel/vdso.c @@ -46,6 +46,14 @@ enum arch_vdso_type { #define VDSO_TYPES (ARM64_VDSO + 1) #endif /* CONFIG_COMPAT_VDSO */ +enum vvar_pages { + VVAR_DATA_PAGE_OFFSET = 0, +#ifdef CONFIG_TIME_NS + VVAR_TIMENS_PAGE_OFFSET = 1, +#endif /* CONFIG_TIME_NS */ + VVAR_NR_PAGES = __VVAR_PAGES, +}; + struct __vdso_abi { const char *name; const char *vdso_code_start; @@ -81,6 +89,12 @@ static union { } vdso_data_store __page_aligned_data; struct vdso_data *vdso_data = vdso_data_store.data; + +struct vdso_data *arch_get_vdso_data(void *vvar_page) +{ + return (struct vdso_data *)(vvar_page); +} + static int __vdso_remap(enum arch_vdso_type arch_index, const struct vm_special_mapping *sm, struct vm_area_struct *new_vma) @@ -182,7 +196,7 @@ static int __setup_additional_pages(enum arch_vdso_type arch_index, vdso_text_len = vdso_lookup[arch_index].vdso_pages << PAGE_SHIFT; /* Be sure to map the data page */ - vdso_mapping_len = vdso_text_len + PAGE_SIZE; + vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE; vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0); if (IS_ERR_VALUE(vdso_base)) { @@ -190,13 +204,13 @@ static int __setup_additional_pages(enum arch_vdso_type arch_index, goto up_fail; } - ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE, + ret = _install_special_mapping(mm, vdso_base, VVAR_NR_PAGES * PAGE_SIZE, VM_READ|VM_MAYREAD|VM_PFNMAP, vdso_lookup[arch_index].dm); if (IS_ERR(ret)) goto up_fail; - vdso_base += PAGE_SIZE; + vdso_base += VVAR_NR_PAGES * PAGE_SIZE; mm->context.vdso = (void *)vdso_base; ret = _install_special_mapping(mm, vdso_base, vdso_text_len, VM_READ|VM_EXEC| diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S index 7ad2d3a0cd48..d808ad31e01f 100644 --- a/arch/arm64/kernel/vdso/vdso.lds.S +++ b/arch/arm64/kernel/vdso/vdso.lds.S @@ -17,7 +17,10 @@ OUTPUT_ARCH(aarch64) SECTIONS { - PROVIDE(_vdso_data = . - PAGE_SIZE); + PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE); +#ifdef CONFIG_TIME_NS + PROVIDE(_timens_data = _vdso_data + PAGE_SIZE); +#endif . = VDSO_LBASE + SIZEOF_HEADERS; .hash : { *(.hash) } :text diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S index a3944927eaeb..06cc60a9630f 100644 --- a/arch/arm64/kernel/vdso32/vdso.lds.S +++ b/arch/arm64/kernel/vdso32/vdso.lds.S @@ -17,7 +17,10 @@ OUTPUT_ARCH(arm) SECTIONS { - PROVIDE_HIDDEN(_vdso_data = . - PAGE_SIZE); + PROVIDE_HIDDEN(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE); +#ifdef CONFIG_TIME_NS + PROVIDE_HIDDEN(_timens_data = _vdso_data + PAGE_SIZE); +#endif . = VDSO_LBASE + SIZEOF_HEADERS; .hash : { *(.hash) } :text diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h index 30c4cb0428d1..3494b5536b63 100644 --- a/include/vdso/datapage.h +++ b/include/vdso/datapage.h @@ -98,6 +98,7 @@ struct vdso_data { * relocation, and this is what we need. */ extern struct vdso_data _vdso_data[CS_BASES] __attribute__((visibility("hidden"))); +extern struct vdso_data _timens_data[CS_BASES] __attribute__((visibility("hidden"))); #endif /* !__ASSEMBLY__ */
Allocate the time namespace page among VVAR pages. Provide __arch_get_timens_vdso_data() helper for VDSO code to get the code-relative position of VVARs on that special page. If a task belongs to a time namespace then the VVAR page which contains the system wide VDSO data is replaced with a namespace specific page which has the same layout as the VVAR page. That page has vdso_data->seq set to 1 to enforce the slow path and vdso_data->clock_mode set to VCLOCK_TIMENS to enforce the time namespace handling path. The extra check in the case that vdso_data->seq is odd, e.g. a concurrent update of the VDSO data is in progress, is not really affecting regular tasks which are not part of a time namespace as the task is spin waiting for the update to finish and vdso_data->seq to become even again. If a time namespace task hits that code path, it invokes the corresponding time getter function which retrieves the real VVAR page, reads host time and then adds the offset for the requested clock which is stored in the special VVAR page. Signed-off-by: Andrei Vagin <avagin@gmail.com> --- arch/arm64/include/asm/vdso.h | 6 ++++++ .../include/asm/vdso/compat_gettimeofday.h | 11 ++++++++++ arch/arm64/include/asm/vdso/gettimeofday.h | 8 ++++++++ arch/arm64/kernel/vdso.c | 20 ++++++++++++++++--- arch/arm64/kernel/vdso/vdso.lds.S | 5 ++++- arch/arm64/kernel/vdso32/vdso.lds.S | 5 ++++- include/vdso/datapage.h | 1 + 7 files changed, 51 insertions(+), 5 deletions(-)