• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Fix bug causing host SLB to be restored incorrectly · 67f8a8c1
    Paul Mackerras authored
    Aneesh Kumar reported seeing host crashes when running recent kernels
    on POWER8.  The symptom was an oops like this:
    
    Unable to handle kernel paging request for data at address 0xf00000000786c620
    Faulting instruction address: 0xc00000000030e1e4
    Oops: Kernel access of bad area, sig: 11 [#1]
    LE SMP NR_CPUS=2048 NUMA PowerNV
    Modules linked in: powernv_op_panel
    CPU: 24 PID: 6663 Comm: qemu-system-ppc Tainted: G        W 4.13.0-rc7-43932-gfc36c59 #2
    task: c000000fdeadfe80 task.stack: c000000fdeb68000
    NIP:  c00000000030e1e4 LR: c00000000030de6c CTR: c000000000103620
    REGS: c000000fdeb6b450 TRAP: 0300   Tainted: G        W        (4.13.0-rc7-43932-gfc36c59)
    MSR:  9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR: 24044428  XER: 20000000
    CFAR: c00000000030e134 DAR: f00000000786c620 DSISR: 40000000 SOFTE: 0
    GPR00: 0000000000000000 c000000fdeb6b6d0 c0000000010bd000 000000000000e1b0
    GPR04: c00000000115e168 c000001fffa6e4b0 c00000000115d000 c000001e1b180386
    GPR08: f000000000000000 c000000f9a8913e0 f00000000786c600 00007fff587d0000
    GPR12: c000000fdeb68000 c00000000fb0f000 0000000000000001 00007fff587cffff
    GPR16: 0000000000000000 c000000000000000 00000000003fffff c000000fdebfe1f8
    GPR20: 0000000000000004 c000000fdeb6b8a8 0000000000000001 0008000000000040
    GPR24: 07000000000000c0 00007fff587cffff c000000fdec20bf8 00007fff587d0000
    GPR28: c000000fdeca9ac0 00007fff587d0000 00007fff587c0000 00007fff587d0000
    NIP [c00000000030e1e4] __get_user_pages_fast+0x434/0x1070
    LR [c00000000030de6c] __get_user_pages_fast+0xbc/0x1070
    Call Trace:
    [c000000fdeb6b6d0] [c00000000139dab8] lock_classes+0x0/0x35fe50 (unreliable)
    [c000000fdeb6b7e0] [c00000000030ef38] get_user_pages_fast+0xf8/0x120
    [c000000fdeb6b830] [c000000000112318] kvmppc_book3s_hv_page_fault+0x308/0xf30
    [c000000fdeb6b960] [c00000000010e10c] kvmppc_vcpu_run_hv+0xfdc/0x1f00
    [c000000fdeb6bb20] [c0000000000e915c] kvmppc_vcpu_run+0x2c/0x40
    [c000000fdeb6bb40] [c0000000000e5650] kvm_arch_vcpu_ioctl_run+0x110/0x300
    [c000000fdeb6bbe0] [c0000000000d6468] kvm_vcpu_ioctl+0x528/0x900
    [c000000fdeb6bd40] [c0000000003bc04c] do_vfs_ioctl+0xcc/0x950
    [c000000fdeb6bde0] [c0000000003bc930] SyS_ioctl+0x60/0x100
    [c000000fdeb6be30] [c00000000000b96c] system_call+0x58/0x6c
    Instruction dump:
    7ca81a14 2fa50000 41de0010 7cc8182a 68c60002 78c6ffe2 0b060000 3cc2000a
    794a3664 390610d8 e9080000 7d485214 <e90a0020> 7d435378 790507e1 408202f0
    ---[ end trace fad4a342d0414aa2 ]---
    
    It turns out that what has happened is that the SLB entry for the
    vmmemap region hasn't been reloaded on exit from a guest, and it has
    the wrong page size.  Then, when the host next accesses the vmemmap
    region, it gets a page fault.
    
    Commit a25bd72b ("powerpc/mm/radix: Workaround prefetch issue with
    KVM", 2017-07-24) modified the guest exit code so that it now only clears
    out the SLB for hash guest.  The code tests the radix flag and puts the
    result in a non-volatile CR field, CR2, and later branches based on CR2.
    
    Unfortunately, the kvmppc_save_tm function, which gets called between
    those two points, modifies all the user-visible registers in the case
    where the guest was in transactional or suspended state, except for a
    few which it restores (namely r1, r2, r9 and r13).  Thus the hash/radix indication in CR2 gets corrupted.
    
    This fixes the problem by re-doing the comparison just before the
    result is needed.  For good measure, this also adds comments next to
    the call sites of kvmppc_save_tm and kvmppc_restore_tm pointing out
    that non-volatile register state will be lost.
    
    Cc: stable@vger.kernel.org # v4.13
    Fixes: a25bd72b ("powerpc/mm/radix: Workaround prefetch issue with KVM")
    Tested-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    67f8a8c1
book3s_hv_rmhandlers.S 77.8 KB