linux-kernel - [RFC 0/2] kvm/x86: more huge page recovery fallout

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Message-ID: <20250226024236.1806294-1-kbusch@meta.com>
Date: Tue, 25 Feb 2025 18:42:36 -0800
From: Keith Busch <kbusch@...a.com>
To: <pbonzini@...hat.com>, <seanjc@...gle.com>, <kvm@...r.kernel.org>
CC: <x86@...nel.org>, <virtualization@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, Keith Busch <kbusch@...nel.org>
Subject: [RFC 0/2] kvm/x86: more huge page recovery fallout

From: Keith Busch <kbusch@...nel.org>

Another corner case on the KVM vhost task!

The crosvm VMM might send signals to its threads that have entered
KVM_RUN. The signal specifically is SIGRTRMIN from here:

  https://github.com/google/crosvm/blob/main/src/crosvm/sys/linux/vcpu.rs#L651

If this happens to occur when the huge page recovery is trying to create
its vhost task, that will fail with ERESTARTNOINTR. Once this happens,
all KVM_RUN calls will fail with ENOMEM despite memory not being the
problem.

This series propogates the error up so we can distinguish that from the
current defaulting to ENOMEM and replaces the call_once since we need to
be able to call it repeatedly due to this condition.

Keith Busch (2):
  vhost: return error instead of NULL on create
  kvm: retry nx_huge_page_recovery_thread creation

 arch/x86/include/asm/kvm_host.h |  3 +--
 arch/x86/kvm/mmu/mmu.c          | 25 ++++++++++---------------
 arch/x86/kvm/x86.c              |  2 +-
 drivers/vhost/vhost.c           |  2 +-
 kernel/vhost_task.c             |  4 ++--
 5 files changed, 15 insertions(+), 21 deletions(-)

-- 
2.43.5