| Message ID | 20241014105912.3207374-19-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Boot-time page size selection for arm64 | expand |
On 10/14/24 at 11:58am, Ryan Roberts wrote: > To prepare for supporting boot-time page size selection, refactor code > to remove assumptions about PAGE_SIZE being compile-time constant. Code > intended to be equivalent when compile-time page size is active. > > Updated BUILD_BUG_ON() to test against limit. > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > --- > > ***NOTE*** > Any confused maintainers may want to read the cover note here for context: > https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/ > > kernel/crash_core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c > index 63cf89393c6eb..978c600a47ac8 100644 > --- a/kernel/crash_core.c > +++ b/kernel/crash_core.c > @@ -465,7 +465,7 @@ static int __init crash_notes_memory_init(void) > * Break compile if size is bigger than PAGE_SIZE since crash_notes > * definitely will be in 2 pages with that. > */ > - BUILD_BUG_ON(size > PAGE_SIZE); > + BUILD_BUG_ON(size > PAGE_SIZE_MIN); This should be OK. While one thing which could happen is if selected size is 64K, PAGE_SIZE_MIN is 4K, it will issue a false-positive warning when compiling while actual it's not a problem during running. Not sure if that could happen on arm64. Anyway, we can check the crash_notes to get why it's so big when it really happens. So, Acked-by: Baoquan He <bhe@redhat.com> > > crash_notes = __alloc_percpu(size, align); > if (!crash_notes) { > -- > 2.43.0 > >
On 15/10/2024 04:47, Baoquan He wrote: > On 10/14/24 at 11:58am, Ryan Roberts wrote: >> To prepare for supporting boot-time page size selection, refactor code >> to remove assumptions about PAGE_SIZE being compile-time constant. Code >> intended to be equivalent when compile-time page size is active. >> >> Updated BUILD_BUG_ON() to test against limit. >> >> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> >> --- >> >> ***NOTE*** >> Any confused maintainers may want to read the cover note here for context: >> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/ >> >> kernel/crash_core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 63cf89393c6eb..978c600a47ac8 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -465,7 +465,7 @@ static int __init crash_notes_memory_init(void) >> * Break compile if size is bigger than PAGE_SIZE since crash_notes >> * definitely will be in 2 pages with that. >> */ >> - BUILD_BUG_ON(size > PAGE_SIZE); >> + BUILD_BUG_ON(size > PAGE_SIZE_MIN); > > This should be OK. While one thing which could happen is if selected size > is 64K, PAGE_SIZE_MIN is 4K, it will issue a false-positive warning when > compiling while actual it's not a problem during running. PAGE_SIZE can only ever be bigger than PAGE_SIZE_MIN if compiling a "boot-time page size" build. And in this case, you need to know that size is small enough to work with any of the boot-time selectable page sizes. Since size (=sizeof(note_buf_t)) is invariant to PAGE_SIZE, we can do this by checking against PAGE_SIZE_MIN. So I don't think this could ever lead to a false-positive. Not sure if > that could happen on arm64. Anyway, we can check the crash_notes to get > why it's so big when it really happens. So, > > Acked-by: Baoquan He <bhe@redhat.com> Thanks! > >> >> crash_notes = __alloc_percpu(size, align); >> if (!crash_notes) { >> -- >> 2.43.0 >> >> >
On 10/15/24 at 12:13pm, Ryan Roberts wrote: > On 15/10/2024 04:47, Baoquan He wrote: > > On 10/14/24 at 11:58am, Ryan Roberts wrote: > >> To prepare for supporting boot-time page size selection, refactor code > >> to remove assumptions about PAGE_SIZE being compile-time constant. Code > >> intended to be equivalent when compile-time page size is active. > >> > >> Updated BUILD_BUG_ON() to test against limit. > >> > >> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > >> --- > >> > >> ***NOTE*** > >> Any confused maintainers may want to read the cover note here for context: > >> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/ > >> > >> kernel/crash_core.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c > >> index 63cf89393c6eb..978c600a47ac8 100644 > >> --- a/kernel/crash_core.c > >> +++ b/kernel/crash_core.c > >> @@ -465,7 +465,7 @@ static int __init crash_notes_memory_init(void) > >> * Break compile if size is bigger than PAGE_SIZE since crash_notes > >> * definitely will be in 2 pages with that. > >> */ > >> - BUILD_BUG_ON(size > PAGE_SIZE); > >> + BUILD_BUG_ON(size > PAGE_SIZE_MIN); > > > > This should be OK. While one thing which could happen is if selected size > > is 64K, PAGE_SIZE_MIN is 4K, it will issue a false-positive warning when > > compiling while actual it's not a problem during running. > > PAGE_SIZE can only ever be bigger than PAGE_SIZE_MIN if compiling a "boot-time > page size" build. And in this case, you need to know that size is small enough > to work with any of the boot-time selectable page sizes. Since size > (=sizeof(note_buf_t)) is invariant to PAGE_SIZE, we can do this by checking > against PAGE_SIZE_MIN. > > So I don't think this could ever lead to a false-positive. Makes sense, thanks for your explanation. > > > Not sure if > > that could happen on arm64. Anyway, we can check the crash_notes to get > > why it's so big when it really happens. So, > > > > Acked-by: Baoquan He <bhe@redhat.com> > > Thanks! > > > > >> > >> crash_notes = __alloc_percpu(size, align); > >> if (!crash_notes) { > >> -- > >> 2.43.0 > >> > >> > > >
diff --git a/kernel/crash_core.c b/kernel/crash_core.c index 63cf89393c6eb..978c600a47ac8 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -465,7 +465,7 @@ static int __init crash_notes_memory_init(void) * Break compile if size is bigger than PAGE_SIZE since crash_notes * definitely will be in 2 pages with that. */ - BUILD_BUG_ON(size > PAGE_SIZE); + BUILD_BUG_ON(size > PAGE_SIZE_MIN); crash_notes = __alloc_percpu(size, align); if (!crash_notes) {
To prepare for supporting boot-time page size selection, refactor code to remove assumptions about PAGE_SIZE being compile-time constant. Code intended to be equivalent when compile-time page size is active. Updated BUILD_BUG_ON() to test against limit. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> --- ***NOTE*** Any confused maintainers may want to read the cover note here for context: https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/ kernel/crash_core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)