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Commit 87da236e authored by Will Deacon's avatar Will Deacon Committed by Catalin Marinas
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arm64: KVM: Add support for VPIPT I-caches 



A VPIPT I-cache has two main properties:

1. Lines allocated into the cache are tagged by VMID and a lookup can
   only hit lines that were allocated with the current VMID.

2. I-cache invalidation from EL1/0 only invalidates lines that match the
   current VMID of the CPU doing the invalidation.

This can cause issues with non-VHE configurations, where the host runs
at EL1 and wants to invalidate I-cache entries for a guest running with
a different VMID. VHE is not affected, because the host runs at EL2 and
I-cache invalidation applies as expected.

This patch solves the problem by invalidating the I-cache when unmapping
a page at stage 2 on a system with a VPIPT I-cache but not running with
VHE enabled. Hopefully this is an obscure enough configuration that the
overhead isn't anything to worry about, although it does mean that the
by-range I-cache invalidation currently performed when mapping at stage
2 can be elided on such systems, because the I-cache will be clean for
the guest VMID following a rollover event.

Acked-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent dda288d7

arch/arm64/include/asm/kvm_mmu.h

+5 −4
Original line number Diff line number Diff line
@@ -242,12 +242,13 @@ static inline void __coherent_cache_guest_page(struct kvm_vcpu *vcpu, 


	kvm_flush_dcache_to_poc(va, size);



	if (!icache_is_aliasing()) {		/* PIPT */

		flush_icache_range((unsigned long)va,

				   (unsigned long)va + size);

	} else {

	if (icache_is_aliasing()) {

		/* any kind of VIPT cache */

		__flush_icache_all();

	} else if (is_kernel_in_hyp_mode() || !icache_is_vpipt()) {

		/* PIPT or VPIPT at EL2 (see comment in __kvm_tlb_flush_vmid_ipa) */

		flush_icache_range((unsigned long)va,

				   (unsigned long)va + size);

	}

}

arch/arm64/kvm/hyp/tlb.c

+22 −0
Original line number Diff line number Diff line
@@ -94,6 +94,28 @@ void __hyp_text __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa) 
	dsb(ish);

	isb();



	/*

	 * If the host is running at EL1 and we have a VPIPT I-cache,

	 * then we must perform I-cache maintenance at EL2 in order for

	 * it to have an effect on the guest. Since the guest cannot hit

	 * I-cache lines allocated with a different VMID, we don't need

	 * to worry about junk out of guest reset (we nuke the I-cache on

	 * VMID rollover), but we do need to be careful when remapping

	 * executable pages for the same guest. This can happen when KSM

	 * takes a CoW fault on an executable page, copies the page into

	 * a page that was previously mapped in the guest and then needs

	 * to invalidate the guest view of the I-cache for that page

	 * from EL1. To solve this, we invalidate the entire I-cache when

	 * unmapping a page from a guest if we have a VPIPT I-cache but

	 * the host is running at EL1. As above, we could do better if

	 * we had the VA.

	 *

	 * The moral of this story is: if you have a VPIPT I-cache, then

	 * you should be running with VHE enabled.

	 */

	if (!has_vhe() && icache_is_vpipt())

		__flush_icache_all();



	__tlb_switch_to_host()(kvm);

}