Re: [PATCH v3 06/15] KVM: arm64: Implement kvm_pgtable_hyp_unmap() at EL2
From: Andrew Walbran <hidden>
Date: 2021-12-08 14:41:10
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On Wed, 8 Dec 2021 at 09:51, Quentin Perret [off-list ref] wrote:
Hi Andrew, On Tuesday 07 Dec 2021 at 14:47:14 (+0000), Andrew Walbran wrote:quoted
On Wed, 1 Dec 2021 at 17:04, 'Quentin Perret' via kernel-team [off-list ref] wrote:quoted
From: Will Deacon <will@kernel.org> Implement kvm_pgtable_hyp_unmap() which can be used to remove hypervisor stage-1 mappings at EL2. Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Quentin Perret <redacted> --- arch/arm64/include/asm/kvm_pgtable.h | 21 ++++++++++ arch/arm64/kvm/hyp/pgtable.c | 63 ++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+)diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h index 027783829584..9d076f36401d 100644 --- a/arch/arm64/include/asm/kvm_pgtable.h +++ b/arch/arm64/include/asm/kvm_pgtable.h@@ -251,6 +251,27 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt); int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys, enum kvm_pgtable_prot prot); +/** + * kvm_pgtable_hyp_unmap() - Remove a mapping from a hypervisor stage-1 page-table. + * @pgt: Page-table structure initialised by kvm_pgtable_hyp_init(). + * @addr: Virtual address from which to remove the mapping. + * @size: Size of the mapping. + * + * The offset of @addr within a page is ignored, @size is rounded-up to + * the next page boundary and @phys is rounded-down to the previous page + * boundary. + * + * TLB invalidation is performed for each page-table entry cleared during the + * unmapping operation and the reference count for the page-table page + * containing the cleared entry is decremented, with unreferenced pages being + * freed. The unmapping operation will stop early if it encounters either an + * invalid page-table entry or a valid block mapping which maps beyond the range + * being unmapped.How is the caller expected to break up the block mapping? Why not handle that within this function?We don't really use block mappings for the hyp stage-1, since pretty much forever (see the loop in pkvm_create_mappings_locked() for ex), so handling it here would be somewhat unnecessary complexity. Handling this in the pgtable code itself (which I assume would mean proactively re-mapping the rest of the range with page-granularity mappings or something along those lines) is tricky because of BBM and concurrency, so I'd rather avoid handling same-level aborts at EL2 and all that mess unless we have a good reason. Is there a use-case where you think that'd be needed?
Aha, I didn't realise that block mappings, but it makes sense in that case. How about adding a note to the function comment here explaining that reasoning? Otherwise it sounds like the caller has to handle it somehow. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel