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KVM: PPC: Book3S HV: Fix KVM_RUN clobbering FP/VEC user registers

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Before running a guest, the host process (e.g., QEMU) FP/VEC registers
are saved if they were being used, similarly to when the kernel uses FP
registers. The guest values are then loaded into regs, and the host
process registers will be restored lazily when it uses FP/VEC.

KVM HV has a bug here: the host process registers do get saved, but the
user MSR bits remain enabled, which indicates the registers are valid
for the process. After they are clobbered by running the guest, this
valid indication causes the host process to take on the FP/VEC register
values of the guest.

Fixes: 34e119c96b ("KVM: PPC: Book3S HV P9: Reduce mtmsrd instructions required to save host SPRs")
Cc: stable@vger.kernel.org # v5.17+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231122025811.2973-1-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2023-11-22 12:58:11 +10:00 committed by Michael Ellerman
parent 5e1d824f9a
commit dc158d23b3
1 changed files with 3 additions and 3 deletions
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6
arch/powerpc/kernel/process.c
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@ -1198,11 +1198,11 @@ void kvmppc_save_user_regs(void)
usermsr = current->thread.regs->msr;
/* Caller has enabled FP/VEC/VSX/TM in MSR */
if (usermsr & MSR_FP)
save_fpu(current);
__giveup_fpu(current);
if (usermsr & MSR_VEC)
save_altivec(current);
__giveup_altivec(current);
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
if (usermsr & MSR_TM) {