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Message-ID: <04DAF94279B88A3F+20240731055755.84082-1-wangyuli@uniontech.com>
Date: Wed, 31 Jul 2024 13:57:55 +0800
From: WangYuli <wangyuli@...ontech.com>
To: pbonzini@...hat.com,
corbet@....net,
zhaotianrui@...ngson.cn,
maobibo@...ngson.cn,
chenhuacai@...nel.org
Cc: kernel@...0n.name,
kvm@...r.kernel.org,
loongarch@...ts.linux.dev,
linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org,
guanwentao@...ontech.com,
Xianglai Li <lixianglai@...ngson.cn>,
WangYuli <wangyuli@...ontech.com>
Subject: [PATCH] Loongarch: KVM: Add KVM hypercalls documentation for LoongArch
From: Bibo Mao <maobibo@...ngson.cn>
Add documentation topic for using pv_virt when running as a guest
on KVM hypervisor.
Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
Signed-off-by: Xianglai Li <lixianglai@...ngson.cn>
Signed-off-by: WangYuli <wangyuli@...ontech.com>
---
Documentation/virt/kvm/index.rst | 1 +
.../virt/kvm/loongarch/hypercalls.rst | 79 +++++++++++++++++++
Documentation/virt/kvm/loongarch/index.rst | 10 +++
MAINTAINERS | 1 +
4 files changed, 91 insertions(+)
create mode 100644 Documentation/virt/kvm/loongarch/hypercalls.rst
create mode 100644 Documentation/virt/kvm/loongarch/index.rst
diff --git a/Documentation/virt/kvm/index.rst b/Documentation/virt/kvm/index.rst
index ad13ec55ddfe..9ca5a45c2140 100644
--- a/Documentation/virt/kvm/index.rst
+++ b/Documentation/virt/kvm/index.rst
@@ -14,6 +14,7 @@ KVM
s390/index
ppc-pv
x86/index
+ loongarch/index
locking
vcpu-requests
diff --git a/Documentation/virt/kvm/loongarch/hypercalls.rst b/Documentation/virt/kvm/loongarch/hypercalls.rst
new file mode 100644
index 000000000000..1679e48d67d2
--- /dev/null
+++ b/Documentation/virt/kvm/loongarch/hypercalls.rst
@@ -0,0 +1,79 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+The LoongArch paravirtual interface
+===================================
+
+KVM hypercalls use the HVCL instruction with code 0x100, and the hypercall
+number is put in a0 and up to five arguments may be placed in a1-a5, the
+return value is placed in v0 (alias with a0).
+
+The code for that interface can be found in arch/loongarch/kvm/*
+
+Querying for existence
+======================
+
+To find out if we're running on KVM or not, cpucfg can be used with index
+CPUCFG_KVM_BASE (0x40000000), cpucfg range between 0x40000000 - 0x400000FF
+is marked as a specially reserved range. All existing and future processors
+will not implement any features in this range.
+
+When Linux is running on KVM, cpucfg with index CPUCFG_KVM_BASE (0x40000000)
+returns magic string "KVM\0"
+
+Once you determined you're running under a PV capable KVM, you can now use
+hypercalls as described below.
+
+KVM hypercall ABI
+=================
+
+Hypercall ABI on KVM is simple, only one scratch register a0 (v0) and at most
+five generic registers used as input parameter. FP register and vector register
+is not used for input register and should not be modified during hypercall.
+Hypercall function can be inlined since there is only one scratch register.
+
+The parameters are as follows:
+
+ ======== ================ ================
+ Register IN OUT
+ ======== ================ ================
+ a0 function number Return code
+ a1 1st parameter -
+ a2 2nd parameter -
+ a3 3rd parameter -
+ a4 4th parameter -
+ a5 5th parameter -
+ ======== ================ ================
+
+Return codes can be as follows:
+
+ ==== =========================
+ Code Meaning
+ ==== =========================
+ 0 Success
+ -1 Hypercall not implemented
+ -2 Hypercall parameter error
+ ==== =========================
+
+KVM Hypercalls Documentation
+============================
+
+The template for each hypercall is:
+1. Hypercall name
+2. Purpose
+
+1. KVM_HCALL_FUNC_PV_IPI
+------------------------
+
+:Purpose: Send IPIs to multiple vCPUs.
+
+- a0: KVM_HCALL_FUNC_PV_IPI
+- a1: lower part of the bitmap of destination physical CPUIDs
+- a2: higher part of the bitmap of destination physical CPUIDs
+- a3: the lowest physical CPUID in bitmap
+
+The hypercall lets a guest send multicast IPIs, with at most 128
+destinations per hypercall. The destinations are represented by a bitmap
+contained in the first two arguments (a1 and a2). Bit 0 of a1 corresponds
+to the physical CPUID in the third argument (a3), bit 1 corresponds to the
+physical ID a3+1, and so on.
diff --git a/Documentation/virt/kvm/loongarch/index.rst b/Documentation/virt/kvm/loongarch/index.rst
new file mode 100644
index 000000000000..83387b4c5345
--- /dev/null
+++ b/Documentation/virt/kvm/loongarch/index.rst
@@ -0,0 +1,10 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+KVM for LoongArch systems
+=========================
+
+.. toctree::
+ :maxdepth: 2
+
+ hypercalls.rst
diff --git a/MAINTAINERS b/MAINTAINERS
index 958e935449e5..8aa5d92b12ee 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12073,6 +12073,7 @@ L: kvm@...r.kernel.org
L: loongarch@...ts.linux.dev
S: Maintained
T: git git://git.kernel.org/pub/scm/virt/kvm/kvm.git
+F: Documentation/virt/kvm/loongarch/
F: arch/loongarch/include/asm/kvm*
F: arch/loongarch/include/uapi/asm/kvm*
F: arch/loongarch/kvm/
--
2.43.4
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