| Message ID | 20220614120231.48165-12-kirill.shutemov@linux.intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | mm, x86/cc: Implement support for unaccepted memory | expand |
... adding kexec folks On 6/14/22 05:02, Kirill A. Shutemov wrote: > On kexec, the target kernel has to know what memory has been accepted. > Information in EFI map is out of date and cannot be used. > > boot_params.unaccepted_memory can be used to pass the bitmap between two > kernels on kexec, but the use-case is not yet implemented. > > Disable kexec on machines with unaccepted memory for now. ... > +static int __init unaccepted_init(void) > +{ > + if (!boot_params.unaccepted_memory) > + return 0; > + > +#ifdef CONFIG_KEXEC_CORE > + /* > + * TODO: Information on memory acceptance status has to be communicated > + * between kernel. > + */ > + pr_warn("Disable kexec: not yet supported on systems with unaccepted memory\n"); > + kexec_load_disabled = 1; > +#endif This looks to be the *only* in-kernel user tweaking kexec_load_disabled. It doesn't feel great to just be disabling kexec like this. Why not just fix it properly? What do the kexec folks think?
Dave Hansen <dave.hansen@intel.com> writes: > ... adding kexec folks > > On 6/14/22 05:02, Kirill A. Shutemov wrote: >> On kexec, the target kernel has to know what memory has been accepted. >> Information in EFI map is out of date and cannot be used. >> >> boot_params.unaccepted_memory can be used to pass the bitmap between two >> kernels on kexec, but the use-case is not yet implemented. >> >> Disable kexec on machines with unaccepted memory for now. > ... >> +static int __init unaccepted_init(void) >> +{ >> + if (!boot_params.unaccepted_memory) >> + return 0; >> + >> +#ifdef CONFIG_KEXEC_CORE >> + /* >> + * TODO: Information on memory acceptance status has to be communicated >> + * between kernel. >> + */ >> + pr_warn("Disable kexec: not yet supported on systems with unaccepted memory\n"); >> + kexec_load_disabled = 1; >> +#endif > > This looks to be the *only* in-kernel user tweaking kexec_load_disabled. > It doesn't feel great to just be disabling kexec like this. Why not > just fix it properly? > > What do the kexec folks think? I didn't realized someone had implemented kexec_load_disabled. I am not particularly happy about that. It looks like an over-broad stick that we will have to support forever. This change looks like it just builds on that bad decision. If people don't want to deal with this situation right now, then I recommend they make this new code and KEXEC conflict at the Kconfig level. That would give serious incentive to adding the missing implementation. If there is some deep and fundamental why this can not be supported then it probably makes sense to put some code in the arch_kexec_load hook that verifies that deep and fundamental reason is present. With the kexec code all we have to verify it works is a little testing and careful code review. Something like this makes code review much harder because the entire kernel has to be checked to see if some random driver without locking changed a variable. Rather than having it apparent that this special case exists when reading through the kexec code. Eric
On Thu, Jun 23, 2022 at 04:48:59PM -0500, Eric W. Biederman wrote: > Dave Hansen <dave.hansen@intel.com> writes: > > > ... adding kexec folks > > > > On 6/14/22 05:02, Kirill A. Shutemov wrote: > >> On kexec, the target kernel has to know what memory has been accepted. > >> Information in EFI map is out of date and cannot be used. > >> > >> boot_params.unaccepted_memory can be used to pass the bitmap between two > >> kernels on kexec, but the use-case is not yet implemented. > >> > >> Disable kexec on machines with unaccepted memory for now. > > ... > >> +static int __init unaccepted_init(void) > >> +{ > >> + if (!boot_params.unaccepted_memory) > >> + return 0; > >> + > >> +#ifdef CONFIG_KEXEC_CORE > >> + /* > >> + * TODO: Information on memory acceptance status has to be communicated > >> + * between kernel. > >> + */ > >> + pr_warn("Disable kexec: not yet supported on systems with unaccepted memory\n"); > >> + kexec_load_disabled = 1; > >> +#endif > > > > This looks to be the *only* in-kernel user tweaking kexec_load_disabled. > > It doesn't feel great to just be disabling kexec like this. Why not > > just fix it properly? Unfortunately, problems with kexec are not limited to the unaccepted memory. Isaku pointed out that MADT CPU wake is also problematic for kexec. It doesn't allow CPU offline so secondary kernel will not be able to wake it up. So additional limitation (as of now) for kexec is !SMP on TDX guest. I guess we can implement CPU offlining by going to a loop that checks mailbox and responds to the command. That loops has to be somehow protected from being overwritten on kexec. Other issues may come up as we actually try to implement it. That's all doable, but feels like a scope creep for unaccepted memory enabling patchset :/ Is it a must for merge consideration? > > What do the kexec folks think? > > I didn't realized someone had implemented kexec_load_disabled. I am not > particularly happy about that. It looks like an over-broad stick that > we will have to support forever. > > This change looks like it just builds on that bad decision. > > If people don't want to deal with this situation right now, then I > recommend they make this new code and KEXEC conflict at the Kconfig > level. That would give serious incentive to adding the missing > implementation. I tried to limit KEXEC on Kconfig level before[1]. Naive approach does not work[2]: WARNING: unmet direct dependencies detected for UNACCEPTED_MEMORY Depends on [n]: EFI [=y] && EFI_STUB [=y] && !KEXEC_CORE [=y] Selected by [y]: - INTEL_TDX_GUEST [=y] && HYPERVISOR_GUEST [=y] && X86_64 [=y] && CPU_SUP_INTEL [=y] && X86_X2APIC [=y] Maybe my Kconfig-fu is not strong enough, I donno. [1] https://lore.kernel.org/all/20220425033934.68551-6-kirill.shutemov@linux.intel.com [2] https://lore.kernel.org/all/YnOjJB8h3ZUR9sLX@zn.tnic > If there is some deep and fundamental why this can not be supported > then it probably makes sense to put some code in the arch_kexec_load > hook that verifies that deep and fundamental reason is present. Sounds straight-forward. I can do this. > With the kexec code all we have to verify it works is a little testing > and careful code review. Something like this makes code review much > harder because the entire kernel has to be checked to see if some random > driver without locking changed a variable. Rather than having it > apparent that this special case exists when reading through the kexec > code. > > Eric >
On Fri, Jun 24, 2022 at 05:00:05AM +0300, Kirill A. Shutemov wrote: > > If there is some deep and fundamental why this can not be supported > > then it probably makes sense to put some code in the arch_kexec_load > > hook that verifies that deep and fundamental reason is present. > > Sounds straight-forward. I can do this. What about the patch below?
On 6/28/22 16:51, Kirill A. Shutemov wrote: > On Fri, Jun 24, 2022 at 05:00:05AM +0300, Kirill A. Shutemov wrote: >>> If there is some deep and fundamental why this can not be supported >>> then it probably makes sense to put some code in the arch_kexec_load >>> hook that verifies that deep and fundamental reason is present. ... > + /* > + * TODO: Information on memory acceptance status has to be communicated > + * between kernel. > + */ So, the deep and fundamental reason is... drum roll... you haven't gotten around to implementing bitmap passing yet?!?!? I have the feeling that wasn't what Eric was looking for.
On Tue, Jun 28, 2022 at 05:10:56PM -0700, Dave Hansen wrote: > On 6/28/22 16:51, Kirill A. Shutemov wrote: > > On Fri, Jun 24, 2022 at 05:00:05AM +0300, Kirill A. Shutemov wrote: > >>> If there is some deep and fundamental why this can not be supported > >>> then it probably makes sense to put some code in the arch_kexec_load > >>> hook that verifies that deep and fundamental reason is present. > ... > > + /* > > + * TODO: Information on memory acceptance status has to be communicated > > + * between kernel. > > + */ > > So, the deep and fundamental reason is... drum roll... you haven't > gotten around to implementing bitmap passing yet?!?!? I have the > feeling that wasn't what Eric was looking for. The deep fundamental reason is that everything cannot be implemented and upstreamed at once.
On Wed, 29 Jun 2022 at 08:59, Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote: > > On Tue, Jun 28, 2022 at 05:10:56PM -0700, Dave Hansen wrote: > > On 6/28/22 16:51, Kirill A. Shutemov wrote: > > > On Fri, Jun 24, 2022 at 05:00:05AM +0300, Kirill A. Shutemov wrote: > > >>> If there is some deep and fundamental why this can not be supported > > >>> then it probably makes sense to put some code in the arch_kexec_load > > >>> hook that verifies that deep and fundamental reason is present. > > ... > > > + /* > > > + * TODO: Information on memory acceptance status has to be communicated > > > + * between kernel. > > > + */ > > > > So, the deep and fundamental reason is... drum roll... you haven't > > gotten around to implementing bitmap passing yet?!?!? I have the > > feeling that wasn't what Eric was looking for. > > The deep fundamental reason is that everything cannot be implemented and > upstreamed at once. If the only thing is to pass bitmap to kexec kernel, since you have reserved the bitmap memory I guess it is straightforward to set the kexec bootparams.unaccepted_memory as the old value. Not sure if there are problems when the decompress code accepts memory again though. for kernel kexec_file_load, refer to function setup_boot_parameters() in arch/x86/kernel/kexec-bzimage64.c for kexec_file_load, for kexec-tools kexec_load code refer to setup_linux_system_parameters() kexec/arch/i386/x86-linux-setup.c Thanks Dave
diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c index bcd56fe82b9e..05e216716690 100644 --- a/arch/x86/mm/unaccepted_memory.c +++ b/arch/x86/mm/unaccepted_memory.c @@ -1,4 +1,5 @@ // SPDX-License-Identifier: GPL-2.0-only +#include <linux/kexec.h> #include <linux/memblock.h> #include <linux/mm.h> #include <linux/pfn.h> @@ -95,3 +96,21 @@ bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end) return ret; } + +static int __init unaccepted_init(void) +{ + if (!boot_params.unaccepted_memory) + return 0; + +#ifdef CONFIG_KEXEC_CORE + /* + * TODO: Information on memory acceptance status has to be communicated + * between kernel. + */ + pr_warn("Disable kexec: not yet supported on systems with unaccepted memory\n"); + kexec_load_disabled = 1; +#endif + + return 0; +} +fs_initcall(unaccepted_init);
On kexec, the target kernel has to know what memory has been accepted. Information in EFI map is out of date and cannot be used. boot_params.unaccepted_memory can be used to pass the bitmap between two kernels on kexec, but the use-case is not yet implemented. Disable kexec on machines with unaccepted memory for now. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/mm/unaccepted_memory.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)