Re: regression: insmod module failed in VM with nvdimm on

[Ard Biesheuvel <ardb@kernel.org>]

On Thu, 1 Dec 2022 at 09:07, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Thu, 1 Dec 2022 at 08:15, chenxiang (M) <chenxiang66@hisilicon.com> wrote:
> >
> > Hi Ard,
> >
> >
> > 在 2022/11/30 16:18, Ard Biesheuvel 写道:
> > > On Wed, 30 Nov 2022 at 08:53, Marc Zyngier <maz@kernel.org> wrote:
> > >> On Wed, 30 Nov 2022 02:52:35 +0000,
> > >> "chenxiang (M)" <chenxiang66@hisilicon.com> wrote:
> > >>> Hi,
> > >>>
> > >>> We boot the VM using following commands (with nvdimm on)  (qemu
> > >>> version 6.1.50, kernel 6.0-r4):
> > >> How relevant is the presence of the nvdimm? Do you observe the failure
> > >> without this?
> > >>
> > >>> qemu-system-aarch64 -machine
> > >>> virt,kernel_irqchip=on,gic-version=3,nvdimm=on  -kernel
> > >>> /home/kernel/Image -initrd /home/mini-rootfs/rootfs.cpio.gz -bios
> > >>> /root/QEMU_EFI.FD -cpu host -enable-kvm -net none -nographic -m
> > >>> 2G,maxmem=64G,slots=3 -smp 4 -append 'rdinit=init console=ttyAMA0
> > >>> ealycon=pl0ll,0x90000000 pcie_ports=native pciehp.pciehp_debug=1'
> > >>> -object memory-backend-ram,id=ram1,size=10G -device
> > >>> nvdimm,id=dimm1,memdev=ram1  -device ioh3420,id=root_port1,chassis=1
> > >>> -device vfio-pci,host=7d:01.0,id=net0,bus=root_port1
> > >>>
> > >>> Then in VM we insmod a module, vmalloc error occurs as follows (kernel
> > >>> 5.19-rc4 is normal, and the issue is still on kernel 6.1-rc4):
> > >>>
> > >>> estuary:/$ insmod /lib/modules/$(uname -r)/hnae3.ko
> > >>> [    8.186563] vmap allocation for size 20480 failed: use
> > >>> vmalloc=<size> to increase size
> > >> Have you tried increasing the vmalloc size to check that this is
> > >> indeed the problem?
> > >>
> > >> [...]
> > >>
> > >>> We git bisect the code, and find the patch c5a89f75d2a ("arm64: kaslr:
> > >>> defer initialization to initcall where permitted").
> > >> I guess you mean commit fc5a89f75d2a instead, right?
> > >>
> > >>> Do you have any idea about the issue?
> > >> I sort of suspect that the nvdimm gets vmap-ed and consumes a large
> > >> portion of the vmalloc space, but you give very little information
> > >> that could help here...
> > >>
> > > Ouch. I suspect what's going on here: that patch defers the
> > > randomization of the module region, so that we can decouple it from
> > > the very early init code.
> > >
> > > Obviously, it is happening too late now, and the randomized module
> > > region is overlapping with a vmalloc region that is in use by the time
> > > the randomization occurs.
> > >
> > > Does the below fix the issue?
> >
> > The issue still occurs, but it seems decrease the probability, before it
> > occured almost every time, after the change, i tried 2-3 times, and it
> > occurs.
> > But i change back "subsys_initcall" to "core_initcall", and i test more
> > than 20 times, and it is still ok.
> >
>
> Thank you for confirming. I will send out a patch today.
>

...but before I do that, could you please check whether the change
below fixes your issue as well?

diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 6ccc7ef600e7c1e1..c8c205b630da1951 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -20,7 +20,11 @@
 #include <asm/sections.h>
 #include <asm/setup.h>

-u64 __ro_after_init module_alloc_base;
+/*
+ * Set a reasonable default for module_alloc_base in case
+ * we end up running with module randomization disabled.
+ */
+u64 __ro_after_init module_alloc_base = (u64)_etext - MODULES_VSIZE;
 u16 __initdata memstart_offset_seed;

 struct arm64_ftr_override kaslr_feature_override __initdata;
@@ -30,12 +34,6 @@ static int __init kaslr_init(void)
        u64 module_range;
        u32 seed;

-       /*
-        * Set a reasonable default for module_alloc_base in case
-        * we end up running with module randomization disabled.
-        */
-       module_alloc_base = (u64)_etext - MODULES_VSIZE;
-
        if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
                pr_info("KASLR disabled on command line\n");
                return 0;

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