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Subject[PATCH 4.13 021/110] KVM: PPC: Book3S HV: Fix bug causing host SLB to be restored incorrectly
Date
4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Mackerras <paulus@ozlabs.org>

commit 67f8a8c1151c9ef3d1285905d1e66ebb769ecdf7 upstream.

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 a25bd72badfa ("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.

Fixes: a25bd72badfa ("powerpc/mm/radix: Workaround prefetch issue with KVM")
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -765,6 +765,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)

#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
BEGIN_FTR_SECTION
+ /*
+ * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+ */
bl kvmppc_restore_tm
END_FTR_SECTION_IFSET(CPU_FTR_TM)
#endif
@@ -1623,6 +1626,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)

#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
BEGIN_FTR_SECTION
+ /*
+ * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+ */
bl kvmppc_save_tm
END_FTR_SECTION_IFSET(CPU_FTR_TM)
#endif
@@ -1742,7 +1748,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
/*
* Are we running hash or radix ?
*/
- beq cr2,3f
+ ld r5, VCPU_KVM(r9)
+ lbz r0, KVM_RADIX(r5)
+ cmpwi cr2, r0, 0
+ beq cr2, 3f

/* Radix: Handle the case where the guest used an illegal PID */
LOAD_REG_ADDR(r4, mmu_base_pid)
@@ -2459,6 +2468,9 @@ _GLOBAL(kvmppc_h_cede) /* r3 = vcpu poi

#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
BEGIN_FTR_SECTION
+ /*
+ * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+ */
ld r9, HSTATE_KVM_VCPU(r13)
bl kvmppc_save_tm
END_FTR_SECTION_IFSET(CPU_FTR_TM)
@@ -2569,6 +2581,9 @@ kvm_end_cede:

#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
BEGIN_FTR_SECTION
+ /*
+ * NOTE THAT THIS TRASHES ALL NON-VOLATILE REGISTERS INCLUDING CR
+ */
bl kvmppc_restore_tm
END_FTR_SECTION_IFSET(CPU_FTR_TM)
#endif

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