From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A57081C750 for ; Fri, 2 Jun 2023 16:20:00 +0000 (UTC) Received: by mail-yb1-f201.google.com with SMTP id 3f1490d57ef6-ba8c3186735so2971369276.3 for ; Fri, 02 Jun 2023 09:20:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1685722799; x=1688314799; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=4E8+zNfn1rJk8U6PDocth2WfbfjiLTYwf3mfdWaR2yU=; b=gWDsLQXMBko5cslhOYtYqHCyQkoSrIwxBgZlMhgc7PNFm+zEUTxO94Bb/6m4V/EXdI ttDq2ZVJ3U/LswNpYO7WaOvKJQ1mU2ohVzru4+1yqUgYvW05Z+rRWP5SJEurktQZ25op YB/K+hiuDlX+gtpUN/hQOEkjouBS4zjKnwcJCF/H7COoAVWeG5994D9XMONrga8GdVyH rJOrqLcrmwMzoWNdKHNiNP3fLnxHVzb0XhtEFp7916G+C9v60v5qYJjg15saFy1OKfe5 fRnGlvd0yd/9HdwMa9oN9ANxKkQfA2K6mQOuAQ3dG+X4EysL8mmVa1H9MXxwN5Gef3Br rN7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685722799; x=1688314799; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=4E8+zNfn1rJk8U6PDocth2WfbfjiLTYwf3mfdWaR2yU=; b=G4A9vGDM7Sjyg0bduY4gkUfaB6/993eOF+TsTaF5HdVyIC4yXB1+7ZRl0OQUjAt7Q5 pWxk3O9FtvZyW35z3qabd0yOWbQjwgqmQhGpOyqg54uNH+SrmK/9hH8kq5qgAh9UhlIT L5G3dqW1Z+qc92O4FqzdV0lde8viRY0+RMzfB+niuNrvBZihWm2K/7eG6gft4UrfiBsB +xlfA4lzFdZc25LITcD2PHMI6xe4EhrWVve3BiqtmOZQ8ZfYoWXM+05iSBZzeNHDgoeN IkmPp9zYLSHgxFNRC+WOz3Ws38me63Cxer+jZNnDsBec+JudI76k62gjDTCaDJUAeD8O NeyA== X-Gm-Message-State: AC+VfDxGHFvnC5Kl89HQhmIF0M8BugMGedpYyZQbiGN6ZR/lDVRG34s4 TJ8TRccwlKBqVRJRUpZcb761xivy/V8hUw== X-Google-Smtp-Source: ACHHUZ7IOKhrQkM5+thZOkEyj7PyCIBHPmI5OcHGabjfs9Y8mO4Rss5CHJYmBbwWqftwew9oXtBqqj0YAR1ilA== X-Received: from laogai.c.googlers.com ([fda3:e722:ac3:cc00:2b:7d90:c0a8:2c9]) (user=amoorthy job=sendgmr) by 2002:a25:e7c6:0:b0:ba8:8fad:c19d with SMTP id e189-20020a25e7c6000000b00ba88fadc19dmr1257767ybh.8.1685722799503; Fri, 02 Jun 2023 09:19:59 -0700 (PDT) Date: Fri, 2 Jun 2023 16:19:14 +0000 In-Reply-To: <20230602161921.208564-1-amoorthy@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20230602161921.208564-1-amoorthy@google.com> X-Mailer: git-send-email 2.41.0.rc0.172.g3f132b7071-goog Message-ID: <20230602161921.208564-10-amoorthy@google.com> Subject: [PATCH v4 09/16] KVM: Introduce KVM_CAP_NOWAIT_ON_FAULT without implementation From: Anish Moorthy To: seanjc@google.com, oliver.upton@linux.dev, kvm@vger.kernel.org, kvmarm@lists.linux.dev Cc: pbonzini@redhat.com, maz@kernel.org, robert.hoo.linux@gmail.com, jthoughton@google.com, amoorthy@google.com, bgardon@google.com, dmatlack@google.com, ricarkol@google.com, axelrasmussen@google.com, peterx@redhat.com, nadav.amit@gmail.com, isaku.yamahata@gmail.com Content-Type: text/plain; charset="UTF-8" Add documentation, memslot flags, useful helper functions, and the actual new capability itself. Memory fault exits on absent mappings are particularly useful for userfaultfd-based postcopy live migration. When many vCPUs fault on a single userfaultfd the faults can take a while to surface to userspace due to having to contend for uffd wait queue locks. Bypassing the uffd entirely by returning information directly to the vCPU exit avoids this contention and improves the fault rate. Suggested-by: James Houghton Signed-off-by: Anish Moorthy --- Documentation/virt/kvm/api.rst | 32 +++++++++++++++++++++++++++++--- include/linux/kvm_host.h | 6 ++++++ include/uapi/linux/kvm.h | 2 ++ tools/include/uapi/linux/kvm.h | 1 + virt/kvm/kvm_main.c | 3 +++ 5 files changed, 41 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 5b24059143b3..9daadbe2c7ed 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -1312,6 +1312,7 @@ yet and must be cleared on entry. /* for kvm_userspace_memory_region::flags */ #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) #define KVM_MEM_READONLY (1UL << 1) + #define KVM_MEM_NOWAIT_ON_FAULT (1UL << 2) This ioctl allows the user to create, modify or delete a guest physical memory slot. Bits 0-15 of "slot" specify the slot id and this value @@ -1342,12 +1343,15 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr be identical. This allows large pages in the guest to be backed by large pages in the host. -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and -KVM_MEM_READONLY. The former can be set to instruct KVM to keep track of +The flags field supports three flags + +1. KVM_MEM_LOG_DIRTY_PAGES: can be set to instruct KVM to keep track of writes to memory within the slot. See KVM_GET_DIRTY_LOG ioctl to know how to -use it. The latter can be set, if KVM_CAP_READONLY_MEM capability allows it, +use it. +2. KVM_MEM_READONLY: can be set, if KVM_CAP_READONLY_MEM capability allows it, to make a new slot read-only. In this case, writes to this memory will be posted to userspace as KVM_EXIT_MMIO exits. +3. KVM_MEM_NOWAIT_ON_FAULT: see KVM_CAP_NOWAIT_ON_FAULT for details. When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of the memory region are automatically reflected into the guest. For example, an @@ -7776,6 +7780,28 @@ userspace may receive "bare" EFAULTs (i.e. exit reason != KVM_EXIT_MEMORY_FAULT) from KVM_RUN for failures which may be resolvable. These should be considered bugs and reported to the maintainers so that annotations can be added. +7.35 KVM_CAP_NOWAIT_ON_FAULT +---------------------------- + +:Architectures: None +:Returns: -EINVAL. + +The presence of this capability indicates that userspace may pass the +KVM_MEM_NOWAIT_ON_FAULT flag to KVM_SET_USER_MEMORY_REGION to cause KVM_RUN +to fail (-EFAULT) in response to page faults for which resolution would require +the faulting thread to sleep. + +The range of guest physical memory causing the fault is advertised to userspace +through KVM_CAP_MEMORY_FAULT_INFO. + +Userspace should determine how best to make the mapping present, then take +appropriate action. For instance establishing the mapping could involve a +MADV_POPULATE_READ|WRITE, in the context of userfaultfd a UFFDIO_COPY|CONTINUE +could be appropriate, etc. After establishing the mapping, userspace can return +to KVM to retry the memory access. + +Attempts to enable this capability directly will fail. + 8. Other capabilities. ====================== diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 69a221f71914..abbc5dd72292 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2297,4 +2297,10 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr) */ inline void kvm_populate_efault_info(struct kvm_vcpu *vcpu, uint64_t gpa, uint64_t len, uint64_t flags); + +static inline bool kvm_slot_nowait_on_fault( + const struct kvm_memory_slot *slot) +{ + return slot->flags & KVM_MEM_NOWAIT_ON_FAULT; +} #endif diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 143abb334f56..595c3d7d36aa 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -102,6 +102,7 @@ struct kvm_userspace_memory_region { */ #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) #define KVM_MEM_READONLY (1UL << 1) +#define KVM_MEM_NOWAIT_ON_FAULT (1UL << 2) /* for KVM_IRQ_LINE */ struct kvm_irq_level { @@ -1198,6 +1199,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_PMU_EVENT_MASKED_EVENTS 226 #define KVM_CAP_COUNTER_OFFSET 227 #define KVM_CAP_MEMORY_FAULT_INFO 228 +#define KVM_CAP_NOWAIT_ON_FAULT 229 #ifdef KVM_CAP_IRQ_ROUTING diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h index 5476fe169921..f64845cd599f 100644 --- a/tools/include/uapi/linux/kvm.h +++ b/tools/include/uapi/linux/kvm.h @@ -102,6 +102,7 @@ struct kvm_userspace_memory_region { */ #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) #define KVM_MEM_READONLY (1UL << 1) +#define KVM_MEM_NOWAIT_ON_FAULT (1UL << 2) /* for KVM_IRQ_LINE */ struct kvm_irq_level { diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 05d6e7e3994d..2c276d4d0821 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1527,6 +1527,9 @@ static int check_memory_region_flags(const struct kvm_userspace_memory_region *m valid_flags |= KVM_MEM_READONLY; #endif + if (kvm_vm_ioctl_check_extension(NULL, KVM_CAP_NOWAIT_ON_FAULT)) + valid_flags |= KVM_MEM_NOWAIT_ON_FAULT; + if (mem->flags & ~valid_flags) return -EINVAL; -- 2.41.0.rc0.172.g3f132b7071-goog