Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK
Hi, On Tue, Nov 28, 2023 at 06:05:20PM +0100, David Hildenbrand wrote: > On 27.11.23 16:04, Alexandru Elisei wrote: > > Hi, > > > > On Fri, Nov 24, 2023 at 08:51:38PM +0100, David Hildenbrand wrote: > > > On 19.11.23 17:57, Alexandru Elisei wrote: > > > > Tag storage memory requires that the tag storage pages used for data are > > > > always migratable when they need to be repurposed to store tags. > > > > > > > > If ARCH_KEEP_MEMBLOCK is enabled, kexec will scan all non-reserved > > > > memblocks to find a suitable location for copying the kernel image. The > > > > kernel image, once loaded, cannot be moved to another location in > > > > physical > > > > memory. The initialization code for the tag storage reserves the > > > > memblocks > > > > for the tag storage pages, which means kexec will not use them, and the > > > > tag > > > > storage pages can be migrated at any time, which is the desired > > > > behaviour. > > > > > > > > However, if ARCH_KEEP_MEMBLOCK is not selected, kexec will not skip a > > > > region unless the memory resource has the > > > > IORESOURCE_SYSRAM_DRIVER_MANAGED > > > > flag, which isn't currently set by the tag storage initialization code. > > > > > > > > Make ARM64_MTE_TAG_STORAGE depend on ARCH_KEEP_MEMBLOCK to make it > > > > explicit > > > > that that the Kconfig option required for it to work correctly. > > > > > > > > Signed-off-by: Alexandru Elisei > > > > --- > > > >arch/arm64/Kconfig | 1 + > > > >1 file changed, 1 insertion(+) > > > > > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > > index 047487046e8f..efa5b7958169 100644 > > > > --- a/arch/arm64/Kconfig > > > > +++ b/arch/arm64/Kconfig > > > > @@ -2065,6 +2065,7 @@ config ARM64_MTE > > > >if ARM64_MTE > > > >config ARM64_MTE_TAG_STORAGE > > > > bool "Dynamic MTE tag storage management" > > > > + depends on ARCH_KEEP_MEMBLOCK > > > > select CONFIG_CMA > > > > help > > > > Adds support for dynamic management of the memory used by the > > > > hardware > > > > > > Doesn't arm64 select that unconditionally? Why is this required then? > > > > I've added this patch to make the dependancy explicit. If, in the future, > > arm64 > > stops selecting ARCH_KEEP_MEMBLOCK, I thinkg it would be very easy to miss > > the > > fact that tag storage depends on it. So this patch is not required per-se, > > it's > > there to document the dependancy. > > I see. Could you add some static_assert / BUILD_BUG_ON instead? I can do that, sure. Thanks, Alex > > I suspect there are plenty other (undocumented) reasons why > ARCH_KEEP_MEMBLOCK has to be enabled for now, and none sets > ARCH_KEEP_MEMBLOCK, I suspect/ > > -- > Cheers, > > David / dhildenb >
Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK
Hi, On Fri, Nov 24, 2023 at 08:51:38PM +0100, David Hildenbrand wrote: > On 19.11.23 17:57, Alexandru Elisei wrote: > > Tag storage memory requires that the tag storage pages used for data are > > always migratable when they need to be repurposed to store tags. > > > > If ARCH_KEEP_MEMBLOCK is enabled, kexec will scan all non-reserved > > memblocks to find a suitable location for copying the kernel image. The > > kernel image, once loaded, cannot be moved to another location in physical > > memory. The initialization code for the tag storage reserves the memblocks > > for the tag storage pages, which means kexec will not use them, and the tag > > storage pages can be migrated at any time, which is the desired behaviour. > > > > However, if ARCH_KEEP_MEMBLOCK is not selected, kexec will not skip a > > region unless the memory resource has the IORESOURCE_SYSRAM_DRIVER_MANAGED > > flag, which isn't currently set by the tag storage initialization code. > > > > Make ARM64_MTE_TAG_STORAGE depend on ARCH_KEEP_MEMBLOCK to make it explicit > > that that the Kconfig option required for it to work correctly. > > > > Signed-off-by: Alexandru Elisei > > --- > > arch/arm64/Kconfig | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 047487046e8f..efa5b7958169 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -2065,6 +2065,7 @@ config ARM64_MTE > > if ARM64_MTE > > config ARM64_MTE_TAG_STORAGE > > bool "Dynamic MTE tag storage management" > > + depends on ARCH_KEEP_MEMBLOCK > > select CONFIG_CMA > > help > > Adds support for dynamic management of the memory used by the hardware > > Doesn't arm64 select that unconditionally? Why is this required then? I've added this patch to make the dependancy explicit. If, in the future, arm64 stops selecting ARCH_KEEP_MEMBLOCK, I thinkg it would be very easy to miss the fact that tag storage depends on it. So this patch is not required per-se, it's there to document the dependancy. Thanks, Alex > > -- > Cheers, > > David / dhildenb >
Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK
On 19.11.23 17:57, Alexandru Elisei wrote: Tag storage memory requires that the tag storage pages used for data are always migratable when they need to be repurposed to store tags. If ARCH_KEEP_MEMBLOCK is enabled, kexec will scan all non-reserved memblocks to find a suitable location for copying the kernel image. The kernel image, once loaded, cannot be moved to another location in physical memory. The initialization code for the tag storage reserves the memblocks for the tag storage pages, which means kexec will not use them, and the tag storage pages can be migrated at any time, which is the desired behaviour. However, if ARCH_KEEP_MEMBLOCK is not selected, kexec will not skip a region unless the memory resource has the IORESOURCE_SYSRAM_DRIVER_MANAGED flag, which isn't currently set by the tag storage initialization code. Make ARM64_MTE_TAG_STORAGE depend on ARCH_KEEP_MEMBLOCK to make it explicit that that the Kconfig option required for it to work correctly. Signed-off-by: Alexandru Elisei --- arch/arm64/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 047487046e8f..efa5b7958169 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -2065,6 +2065,7 @@ config ARM64_MTE if ARM64_MTE config ARM64_MTE_TAG_STORAGE bool "Dynamic MTE tag storage management" + depends on ARCH_KEEP_MEMBLOCK select CONFIG_CMA help Adds support for dynamic management of the memory used by the hardware Doesn't arm64 select that unconditionally? Why is this required then? -- Cheers, David / dhildenb
[PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK
Tag storage memory requires that the tag storage pages used for data are always migratable when they need to be repurposed to store tags. If ARCH_KEEP_MEMBLOCK is enabled, kexec will scan all non-reserved memblocks to find a suitable location for copying the kernel image. The kernel image, once loaded, cannot be moved to another location in physical memory. The initialization code for the tag storage reserves the memblocks for the tag storage pages, which means kexec will not use them, and the tag storage pages can be migrated at any time, which is the desired behaviour. However, if ARCH_KEEP_MEMBLOCK is not selected, kexec will not skip a region unless the memory resource has the IORESOURCE_SYSRAM_DRIVER_MANAGED flag, which isn't currently set by the tag storage initialization code. Make ARM64_MTE_TAG_STORAGE depend on ARCH_KEEP_MEMBLOCK to make it explicit that that the Kconfig option required for it to work correctly. Signed-off-by: Alexandru Elisei --- arch/arm64/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 047487046e8f..efa5b7958169 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -2065,6 +2065,7 @@ config ARM64_MTE if ARM64_MTE config ARM64_MTE_TAG_STORAGE bool "Dynamic MTE tag storage management" + depends on ARCH_KEEP_MEMBLOCK select CONFIG_CMA help Adds support for dynamic management of the memory used by the hardware -- 2.42.1
