Messages in this thread | | | Date | Fri, 21 Jan 2022 15:17:01 +0100 | Subject | Re: [PATCH v2 0/7] kvm: fix latent guest entry/exit bugs | From | Christian Borntraeger <> |
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Am 21.01.22 um 10:53 schrieb Christian Borntraeger: > Am 20.01.22 um 16:14 schrieb Christian Borntraeger: >> >> >> Am 20.01.22 um 13:03 schrieb Mark Rutland: >>> On Thu, Jan 20, 2022 at 12:28:09PM +0100, Paolo Bonzini wrote: >>>> On 1/19/22 20:22, Mark Rutland wrote: >>>>> I wonder, is the s390 guest entry/exit*preemptible* ? >>>>> >>>>> If a timer IRQ can preempt in the middle of the EQS, we wouldn't balance >>>>> things before a ctx-switch to the idle thread, which would then be able >>>>> to hit this. >>>>> >>>>> I'll need to go audit the other architectures for similar. >>>> >>>> They don't enable interrupts in the entry/exit path so they should be okay. >>> >>> True. >>> >>> So it sounds like for s390 adding an explicit preempt_{disable,enable}() is the >>> right thing to do. I'll add that and explanatory commentary. >> >> That would not be trivial I guess. We do allow (and need) page faults on sie for guest >> demand paging and >> >> this piece of arch/s390/mm/fault.c >> >> case GMAP_FAULT: >> if (faulthandler_disabled() || !mm) >> goto out; >> break; >> } >> >> would no longer work since faulthandler_disabled checks for the preempt count. >> > > > Something like this > > > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c > index d30f5986fa85..1c7d45346e12 100644 > --- a/arch/s390/mm/fault.c > +++ b/arch/s390/mm/fault.c > @@ -385,10 +385,18 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access) > return 0; > goto out; > case USER_FAULT: > - case GMAP_FAULT: > if (faulthandler_disabled() || !mm) > goto out; > break; > + /* > + * We know that we interrupted SIE and we are not in a IRQ. > + * preemption might be disabled thus checking for in_atomic > + * would result in failures > + */ > + case GMAP_FAULT: > + if (pagefault_disabled() || !mm) > + goto out; > + break; > } > > perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); > > seems to work with preemption disabled around sie. Not sure yet if this is correct.
No it does not work. scheduling while preemption is disabled. [ 1880.448663] BUG: scheduling while atomic: qemu-system-s39/1806/0x00000002 [ 1880.448674] INFO: lockdep is turned off. [ 1880.448676] Modules linked in: kvm nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables nfnetlink sunrpc mlx5_ib ib_uverbs s390_trng ib_core genwqe_card crc_itu_t vfio_ccw mdev vfio_iommu_type1 eadm_sch vfio zcrypt_cex4 sch_fq_codel configfs ip_tables x_tables mlx5_core ghash_s390 prng aes_s390 des_s390 libdes sha3_512_s390 sha3_256_s390 sha512_s390 sha256_s390 sha1_s390 sha_common pkey zcrypt rng_core autofs4 [ 1880.448730] Preemption disabled at: [ 1880.448731] [<000003ff8070da88>] ckc_irq_pending+0x30/0xe0 [kvm] [ 1880.448778] CPU: 47 PID: 1806 Comm: qemu-system-s39 Tainted: G W 5.16.0-00007-g89e9021389e2-dirty #15 [ 1880.448782] Hardware name: IBM 3906 M04 704 (LPAR) [ 1880.448784] Call Trace: [ 1880.448785] [<000000000bf001d6>] dump_stack_lvl+0x8e/0xc8 [ 1880.448794] [<000000000b26e08a>] __schedule_bug+0xe2/0xf8 [ 1880.448801] [<000000000b26e212>] schedule_debug+0x172/0x1a8 [ 1880.448804] [<000000000bf0bcae>] __schedule+0x56/0x8b0 [ 1880.448808] [<000000000bf0c570>] schedule+0x68/0x110 [ 1880.448811] [<000000000bf13e76>] schedule_timeout+0x106/0x160 [ 1880.448815] [<000000000bf0ddf2>] wait_for_completion+0xc2/0x110 [ 1880.448818] [<000000000b258674>] __flush_work+0xd4/0x118 [ 1880.448823] [<000000000b4e3c88>] __drain_all_pages+0x218/0x308 [ 1880.448829] [<000000000b4ec3bc>] __alloc_pages_slowpath.constprop.0+0x5bc/0xc98 [ 1880.448832] [<000000000b4ece5c>] __alloc_pages+0x3c4/0x448 [ 1880.448835] [<000000000b5143cc>] alloc_pages_vma+0x9c/0x360 [ 1880.448841] [<000000000b4c0d6e>] do_swap_page+0x66e/0xca0 [ 1880.448845] [<000000000b4c3012>] __handle_mm_fault+0x29a/0x4b0 [ 1880.448869] [<000000000b4c33ac>] handle_mm_fault+0x184/0x3a8 [ 1880.448872] [<000000000b2062ce>] do_exception+0x136/0x490 [ 1880.448877] [<000000000b206b9a>] do_dat_exception+0x2a/0x50 [ 1880.448880] [<000000000bf03650>] __do_pgm_check+0x120/0x1f0 [ 1880.448882] [<000000000bf164ee>] pgm_check_handler+0x11e/0x180 [ 1880.448885] [<000000000bf16298>] sie_exit+0x0/0x48 [ 1880.448888] ([<000003ff8071e954>] kvm_s390_enter_exit_sie+0x64/0x98 [kvm]) [ 1880.448910] [<000003ff807061fa>] __vcpu_run+0x2a2/0x5b8 [kvm] [ 1880.448931] [<000003ff807069ba>] kvm_arch_vcpu_ioctl_run+0x10a/0x270 [kvm] [ 1880.448953] [<000003ff806ed02c>] kvm_vcpu_ioctl+0x27c/0xa40 [kvm] [ 1880.448975] [<000000000b58b5c6>] __s390x_sys_ioctl+0xbe/0x100 [ 1880.448982] [<000000000bf038fa>] __do_syscall+0x1da/0x208 [ 1880.448984] [<000000000bf16362>] system_call+0x82/0xb0
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