Hi Will, On 2018/6/21 10:18, Will Deacon wrote: > On Thu, Jun 21, 2018 at 09:38:53AM +0100, James Morse wrote: >> On 20/06/18 17:25, Wei Xu wrote: >>> [ 0.042421] Insufficient stack space to handle exception! >>> [ 0.042423] ESR: 0x96000046 -- DABT (current EL) >>> [ 0.043730] FAR: 0xffff0000093a80e0 >>> [ 0.044714] Task stack: [0xffff0000093a8000..0xffff0000093ac000] >> >> This was a level 2 translation fault on a write, to an address that is within >> the stack.... >> >> >>> [ 0.051113] IRQ stack: [0xffff000008000000..0xffff000008004000] >>> [ 0.057610] Overflow stack: [0xffff80003efce2f0..0xffff80003efcf2f0] >>> [ 0.064003] CPU: 0 PID: 12 Comm: migration/0 Not tainted >>> 4.17.0-45865-g2b31fe7-dirty #10 >>> [ 0.072201] Hardware name: linux,dummy-virt (DT) >> >>> [ 0.076797] pstate: 604003c5 (nZCv DAIF +PAN -UAO) >>> [ 0.081727] pc : el1_sync+0x0/0xb0 >> >> ... from the vectors. >> >> >>> [ 0.085217] lr : kpti_install_ng_mappings+0x120/0x214 >> >> What I think is happening is: we come out of the kpti idmap with the stack >> unmapped. Shortly after we access the stack, which faults. el1_sync faults as >> well when it tries to push the registers to the stack, and we keep going >> until >> we overflow the stack. >> >> I can't reproduce this with kvmtool or qemu in the model. > > Hmm, one thing that occurs to me is that the kpti_install_ng_mappings() > code leaves the nG bit set in table entries, which is actually IGNORED in > the architecture. > > Wei -- does the diff below help at all? Make sure you disable CONFIG_KASAN, > otherwise your kernel will take an age to boot.
Yes, amazing! This patch resolved the issue. I have tested 50 times and can not reproduce the issue any more. Could you please tell more why this patch works? Thanks! Best Regards, Wei > > Will > > --->8 > > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S > index 5f9a73a4452c..70d9e98467ca 100644 > --- a/arch/arm64/mm/proc.S > +++ b/arch/arm64/mm/proc.S > @@ -272,8 +272,8 @@ ENTRY(idmap_kpti_install_ng_mappings) > add end_pgdp, cur_pgdp, #(PTRS_PER_PGD * 8) > do_pgd: __idmap_kpti_get_pgtable_ent pgd > tbnz pgd, #1, walk_puds > -next_pgd: > __idmap_kpti_put_pgtable_ent_ng pgd > +next_pgd: > skip_pgd: > add cur_pgdp, cur_pgdp, #8 > cmp cur_pgdp, end_pgdp > @@ -302,8 +302,8 @@ walk_puds: > add end_pudp, cur_pudp, #(PTRS_PER_PUD * 8) > do_pud: __idmap_kpti_get_pgtable_ent pud > tbnz pud, #1, walk_pmds > -next_pud: > __idmap_kpti_put_pgtable_ent_ng pud > +next_pud: > skip_pud: > add cur_pudp, cur_pudp, 8 > cmp cur_pudp, end_pudp > @@ -323,8 +323,8 @@ walk_pmds: > add end_pmdp, cur_pmdp, #(PTRS_PER_PMD * 8) > do_pmd: __idmap_kpti_get_pgtable_ent pmd > tbnz pmd, #1, walk_ptes > -next_pmd: > __idmap_kpti_put_pgtable_ent_ng pmd > +next_pmd: > skip_pmd: > add cur_pmdp, cur_pmdp, #8 > cmp cur_pmdp, end_pmdp > > . >
