[ Trivial comments inline. You can feel free to ignore them since I know almost nothing about loongarch. ] On 2024/8/26 13:47, Dandan Zhang wrote: > From: Bibo Mao <maobibo@xxxxxxxxxxx> > > Add documentation topic for using pv_virt when running as a guest > on KVM hypervisor. > > Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx> > Signed-off-by: Xianglai Li <lixianglai@xxxxxxxxxxx> > Co-developed-by: Mingcong Bai <jeffbai@xxxxxxx> > Signed-off-by: Mingcong Bai <jeffbai@xxxxxxx> > Link: https://lore.kernel.org/all/5c338084b1bcccc1d57dce9ddb1e7081@xxxxxxx/ > Signed-off-by: Dandan Zhang <zhangdandan@xxxxxxxxxxxxx> > --- > Documentation/virt/kvm/index.rst | 1 + > .../virt/kvm/loongarch/hypercalls.rst | 86 +++++++++++++++++++ > Documentation/virt/kvm/loongarch/index.rst | 10 +++ > MAINTAINERS | 1 + > 4 files changed, 98 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..58168dc7166c > --- /dev/null > +++ b/Documentation/virt/kvm/loongarch/hypercalls.rst > @@ -0,0 +1,86 @@ > +.. 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. Up to five arguments may be placed in registers a1 - a5. > +The return value is placed in v0 (an alias of a0). > + > +Source code for this interface can be found in arch/loongarch/kvm*. > + > +Querying for existence > +====================== > + > +To determine if the host is running on KVM, we can utilize the cpucfg() > +function at index CPUCFG_KVM_BASE (0x40000000). > + > +The CPUCPU_KVM_BASE range, spanning from 0x40000000 to 0x400000FF, The > +CPUCPU_KVM_BASE range between 0x40000000 - 0x400000FF is marked as reserved. What is CPUCPU_KVM_BASE? Grepping it in the code shows nothing. > +Consequently, all current and future processors will not implement any > +feature within this range. > + > +On a KVM-virtualized Linux system, a read operation on cpucfg() at index > +CPUCFG_KVM_BASE (0x40000000) returns the magic string 'KVM\0'. > + > +Once you have determined that your host is running on a paravirtualization- > +capable KVM, you may now use hypercalls as described below. > + > +KVM hypercall ABI > +================= > + > +The KVM hypercall ABI is simple, with one scratch register a0 (v0) and at most > +five generic registers (a1 - a5) used as input parameters. The FP (Floating- > +point) and vector registers are not utilized as input registers and must > +remain unmodified during a hypercall. > + > +Hypercall functions can be inlined as it only uses 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 - > + ======== ================ ================ Please consistently use tab. > + > +The return codes may be one of the following: > + > + ==== ========================= > + Code Meaning > + ==== ========================= > + 0 Success > + -1 Hypercall not implemented > + -2 Bad Hypercall parameter > + ==== ========================= > + > +KVM Hypercalls Documentation > +============================ > + > +The template for each hypercall is as follows: > + > +1. Hypercall name > +2. Purpose > + > +1. KVM_HCALL_FUNC_PV_IPI Is it still a work-in-progress thing? I don't see it in mainline. > +------------------------ > + > +:Purpose: Send IPIs to multiple vCPUs. > + > +- a0: KVM_HCALL_FUNC_PV_IPI > +- a1: Lower part of the bitmap for destination physical CPUIDs > +- a2: Higher part of the bitmap for destination physical CPUIDs > +- a3: The lowest physical CPUID in the bitmap - Is it a feature that implements IPI broadcast with a PV method? - Don't you need to *at least* specify which IPI to send by issuing this hypercall? But again, as I said I know nothing about loongarch. I might have missed some obvious points. > + > +The hypercall lets a guest send multiple IPIs (Inter-Process Interrupts) with > +at most 128 destinations per hypercall.The destinations are represented in a ^ Add a blank space. > +bitmap contained in the first two input registers (a1 and a2). > + > +Bit 0 of a1 corresponds to the physical CPUID in the third input register (a3) > +and bit 1 corresponds to the physical CPUID in a3+1 (a4), and so on. This looks really confusing. "Bit 63 of a1 corresponds to the physical CPUID in a3+63 (a66)"? Zenghui
