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KVM: PPC: Book3S HV P9: Comment and fix MMU context switching code

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Tighten up partition switching code synchronisation and comments.

In particular, hwsync ; isync is required after the last access that is
performed in the context of a partition, before the partition is
switched away from.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-40-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-11-23 19:52:17 +10:00 committed by Michael Ellerman
parent 5236756d04
commit cf3b16cfa6
3 changed files with 42 additions and 13 deletions
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11
arch/powerpc/kvm/book3s_64_entry.S
View File

@ -374,11 +374,16 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_RADIX)
BEGIN_FTR_SECTION
mtspr SPRN_DAWRX1,r10
END_FTR_SECTION_IFSET(CPU_FTR_DAWR1)
mtspr SPRN_PID,r10
/*
* Switch to host MMU mode
* Switch to host MMU mode (don't have the real host PID but we aren't
* going back to userspace).
*/
hwsync
isync
mtspr SPRN_PID,r10
ld r10, HSTATE_KVM_VCPU(r13)
ld r10, VCPU_KVM(r10)
lwz r10, KVM_HOST_LPID(r10)
@ -389,6 +394,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_DAWR1)
ld r10, KVM_HOST_LPCR(r10)
mtspr SPRN_LPCR,r10
isync
/*
* Set GUEST_MODE_NONE so the handler won't branch to KVM, and clear
* MSR_RI in r12 ([H]SRR1) so the handler won't try to return.

4
arch/powerpc/kvm/book3s_64_mmu_radix.c
View File

@ -57,6 +57,8 @@ unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid,
preempt_disable();
asm volatile("hwsync" ::: "memory");
isync();
/* switch the lpid first to avoid running host with unallocated pid */
old_lpid = mfspr(SPRN_LPID);
if (old_lpid != lpid)
@ -75,6 +77,8 @@ unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid,
ret = __copy_to_user_inatomic((void __user *)to, from, n);
pagefault_enable();
asm volatile("hwsync" ::: "memory");
isync();
/* switch the pid first to avoid running host with unallocated pid */
if (quadrant == 1 && pid != old_pid)
mtspr(SPRN_PID, old_pid);

40
arch/powerpc/kvm/book3s_hv_p9_entry.c
View File

@ -531,17 +531,19 @@ static void switch_mmu_to_guest_radix(struct kvm *kvm, struct kvm_vcpu *vcpu, u6
lpid = nested ? nested->shadow_lpid : kvm->arch.lpid;
/*
* All the isync()s are overkill but trivially follow the ISA
* requirements. Some can likely be replaced with justification
* comment for why they are not needed.
* Prior memory accesses to host PID Q3 must be completed before we
* start switching, and stores must be drained to avoid not-my-LPAR
* logic (see switch_mmu_to_host).
*/
asm volatile("hwsync" ::: "memory");
isync();
mtspr(SPRN_LPID, lpid);
isync();
mtspr(SPRN_LPCR, lpcr);
isync();
mtspr(SPRN_PID, vcpu->arch.pid);
isync();
/*
* isync not required here because we are HRFID'ing to guest before
* any guest context access, which is context synchronising.
*/
}
static void switch_mmu_to_guest_hpt(struct kvm *kvm, struct kvm_vcpu *vcpu, u64 lpcr)
@ -551,25 +553,41 @@ static void switch_mmu_to_guest_hpt(struct kvm *kvm, struct kvm_vcpu *vcpu, u64
lpid = kvm->arch.lpid;
/*
* See switch_mmu_to_guest_radix. ptesync should not be required here
* even if the host is in HPT mode because speculative accesses would
* not cause RC updates (we are in real mode).
*/
asm volatile("hwsync" ::: "memory");
isync();
mtspr(SPRN_LPID, lpid);
mtspr(SPRN_LPCR, lpcr);
mtspr(SPRN_PID, vcpu->arch.pid);
for (i = 0; i < vcpu->arch.slb_max; i++)
mtslb(vcpu->arch.slb[i].orige, vcpu->arch.slb[i].origv);
isync();
/*
* isync not required here, see switch_mmu_to_guest_radix.
*/
}
static void switch_mmu_to_host(struct kvm *kvm, u32 pid)
{
/*
* The guest has exited, so guest MMU context is no longer being
* non-speculatively accessed, but a hwsync is needed before the
* mtLPIDR / mtPIDR switch, in order to ensure all stores are drained,
* so the not-my-LPAR tlbie logic does not overlook them.
*/
asm volatile("hwsync" ::: "memory");
isync();
mtspr(SPRN_PID, pid);
isync();
mtspr(SPRN_LPID, kvm->arch.host_lpid);
isync();
mtspr(SPRN_LPCR, kvm->arch.host_lpcr);
isync();
/*
* isync is not required after the switch, because mtmsrd with L=0
* is performed after this switch, which is context synchronising.
*/
if (!radix_enabled())
slb_restore_bolted_realmode();