x86/kvm: Update the comment about asynchronous page fault in exc_page_fault() (66af4f5c) · Commits · 戴 / test

KVM was switched to interrupt-based mechanism for 'page ready' event delivery in Linux-5.8 (see commit ("KVM: x86: interrupt based APF 'page ready' event delivery")) and #PF (ab)use for 'page ready' event delivery was removed. Linux guest switched to this new mechanism exclusively in 5.9 (see commit ("KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery")) so it is not possible to get #PF for a 'page ready' event even when the guest is running on top of an older KVM (APF mechanism won't be enabled). Update the comment in exc_page_fault() to reflect the new reality. Signed-off-by:

Vitaly Kuznetsov <vkuznets@redhat.com> Message-Id: <20201002154313.1505327-1-vkuznets@redhat.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/mm/fault.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -1446,11 +1446,14 @@ DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
		prefetchw(&current->mm->mmap_lock);

		/*
		* KVM has two types of events that are, logically, interrupts, but
		* are unfortunately delivered using the #PF vector. These events are
		* "you just accessed valid memory, but the host doesn't have it right
		* now, so I'll put you to sleep if you continue" and "that memory
		* you tried to access earlier is available now."
		* KVM uses #PF vector to deliver 'page not present' events to guests
		* (asynchronous page fault mechanism). The event happens when a
		* userspace task is trying to access some valid (from guest's point of
		* view) memory which is not currently mapped by the host (e.g. the
		* memory is swapped out). Note, the corresponding "page ready" event
		* which is injected when the memory becomes available, is delived via
		* an interrupt mechanism and not a #PF exception
		* (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()).
		*
		* We are relying on the interrupted context being sane (valid RSP,
		* relevant locks not held, etc.), which is fine as long as the

Admin message