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KVM: PPC: Book3S HV: Prevent POWER7/8 TLB flush flushing SLB

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The POWER9 ERAT flush instruction is a SLBIA with IH=7, which is a
reserved value on POWER7/8. On POWER8 this invalidates the SLB entries
above index 0, similarly to SLBIA IH=0.

If the SLB entries are invalidated, and then the guest is bypassed, the
host SLB does not get re-loaded, so the bolted entries above 0 will be
lost. This can result in kernel stack access causing a SLB fault.

Kernel stack access causing a SLB fault was responsible for the infamous
mega bug (search "Fix SLB reload bug"). Although since commit
48e7b76957 ("powerpc/64s/hash: Convert SLB miss handlers to C") that
starts using the kernel stack in the SLB miss handler, it might only
result in an infinite loop of SLB faults. In any case it's a bug.

Fix this by only executing the instruction on >= POWER9 where IH=7 is
defined not to invalidate the SLB. POWER7/8 don't require this ERAT
flush.

Fixes: 5008711259 ("KVM: PPC: Book3S HV: Invalidate ERAT when flushing guest TLB entries")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211119031627.577853-1-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-11-19 13:16:27 +10:00 committed by Michael Ellerman
parent 1360572566
commit cf0b0e3712
1 changed files with 4 additions and 1 deletions
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5
arch/powerpc/kvm/book3s_hv_builtin.c
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@ -695,6 +695,7 @@ static void flush_guest_tlb(struct kvm *kvm)
"r" (0) : "memory");
}
asm volatile("ptesync": : :"memory");
// POWER9 congruence-class TLBIEL leaves ERAT. Flush it now.
asm volatile(PPC_RADIX_INVALIDATE_ERAT_GUEST : : :"memory");
} else {
for (set = 0; set < kvm->arch.tlb_sets; ++set) {
@ -705,7 +706,9 @@ static void flush_guest_tlb(struct kvm *kvm)
rb += PPC_BIT(51); /* increment set number */
}
asm volatile("ptesync": : :"memory");
asm volatile(PPC_ISA_3_0_INVALIDATE_ERAT : : :"memory");
// POWER9 congruence-class TLBIEL leaves ERAT. Flush it now.
if (cpu_has_feature(CPU_FTR_ARCH_300))
asm volatile(PPC_ISA_3_0_INVALIDATE_ERAT : : :"memory");
}
}