linux-kernel - [PATCH RFC 3/4] kvm: Add new pfn error KVM_PFN_ERR

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Message-Id: <20220617014147.7299-4-peterx@redhat.com>
Date:   Thu, 16 Jun 2022 21:41:46 -0400
From:   Peter Xu <peterx@...hat.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Linux MM Mailing List <linux-mm@...ck.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, peterx@...hat.com
Subject: [PATCH RFC 3/4] kvm: Add new pfn error KVM_PFN_ERR_INTR

Add one new PFN error type to show when we cannot finish fetching the PFN
due to interruptions.  For example, by receiving a generic signal.

This prepares KVM to be able to respond to SIGUSR1 (for QEMU that's the
SIGIPI) even during e.g. handling an userfaultfd page fault.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 include/linux/kvm_host.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b646b6fcaec6..4f84a442f67f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -96,6 +96,7 @@
 #define KVM_PFN_ERR_FAULT	(KVM_PFN_ERR_MASK)
 #define KVM_PFN_ERR_HWPOISON	(KVM_PFN_ERR_MASK + 1)
 #define KVM_PFN_ERR_RO_FAULT	(KVM_PFN_ERR_MASK + 2)
+#define KVM_PFN_ERR_INTR	(KVM_PFN_ERR_MASK + 3)
 
 /*
  * error pfns indicate that the gfn is in slot but faild to
@@ -106,6 +107,16 @@ static inline bool is_error_pfn(kvm_pfn_t pfn)
 	return !!(pfn & KVM_PFN_ERR_MASK);
 }
 
+/*
+ * When KVM_PFN_ERR_INTR is returned, it means we're interrupted during
+ * fetching the PFN (e.g. a signal might have arrived), so we may want to
+ * retry at some later point and kick the userspace to handle the signal.
+ */
+static inline bool is_intr_pfn(kvm_pfn_t pfn)
+{
+	return pfn == KVM_PFN_ERR_INTR;
+}
+
 /*
  * error_noslot pfns indicate that the gfn can not be
  * translated to pfn - it is not in slot or failed to
-- 
2.32.0