Re: [RFC PATCH v11 08/29] KVM: Introduce per-page memory attributes
From: Sean Christopherson <seanjc@google.com>
Date: 2023-08-14 21:55:51
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kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-fsdevel, linux-mips, linux-mm, linux-riscv, linuxppc-dev, lkml
On Mon, Aug 14, 2023, Binbin Wu wrote:
On 7/19/2023 7:44 AM, Sean Christopherson wrote:quoted
+ struct kvm_mmu_notifier_range post_set_range = { + .start = start, + .end = end, + .arg.attributes = attributes, + .handler = kvm_arch_post_set_memory_attributes, + .on_lock = (void *)kvm_null_fn, + .on_unlock = kvm_mmu_invalidate_end, + .may_block = true, + }; + unsigned long i; + void *entry; + int r; + + entry = attributes ? xa_mk_value(attributes) : NULL;Why attributes of value 0 is considered not a value? Is it because 0 is not a valid value when RWX is considered in the future?
0 values don't require an entry in the xarray, i.e. don't need to be stored and so don't consume memory. The potential conflict with a RWX=0 entry has already been noted, but we'll cross that bridge when we get to it, e.g. KVM can easily support RWX=0 by using an internal "valid" flag.
Both the changelog and the document added mention that the address and size of attrs will be updated to "reflect the actual pages of the memory range have been successfully set to the attributes", but it doesn't.
Yeah, on the todo list, all of the changelogs are horribly stale.