From 66af4f5cb1ee44c41a8433877c859d4b3f922f83 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Fri, 2 Oct 2020 17:43:13 +0200 Subject: [PATCH] x86/kvm: Update the comment about asynchronous page fault in exc_page_fault() KVM was switched to interrupt-based mechanism for 'page ready' event delivery in Linux-5.8 (see commit 2635b5c4a0e4 ("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 b1d405751cd5 ("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 Message-Id: <20201002154313.1505327-1-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini --- arch/x86/mm/fault.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 6e3e8a124903..3cf77592ac54 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1446,11 +1446,14 @@ DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) prefetchw(¤t->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 -- GitLab