Re: [PATCH 1/1] KVM: Add KVM_GET_REG_LIST ioctl for LoongArch
From: Bibo Mao
Date: Mon Jan 26 2026 - 04:38:31 EST
On 2026/1/26 下午4:54, liushuyu wrote:
Hi Bibo,Remember to add such lines in function kvm_init_gcsr_flag() in the next round, since MSGINT CSR registers are missing here.
Understood. I will post a v2 patch, and we can continue the discussion
On 2026/1/26 下午12:22, liushuyu wrote:
Hi Bibo,Firstly I do not know how to use ioctl command KVM_GET_REG_LIST in VMM
On 2026/1/26 上午11:38, liushuyu wrote:
Hi Bibo,It will be better if CSR register list can be categorized, for example
Did you mean we should only return the CSR registers initialized in
On 2026/1/25 下午1:43, Zixing Liu wrote:
This ioctl can be used by userspace applications to determine whichCSR_MAX_NUMS is max number of accessible CSR registers, instead only
(special) registers are get/set-able.
This can be very useful for cross-platform VMMs so that they do not
have
to hardcode register indices for each supported architectures.
Signed-off-by: Zixing Liu <liushuyu@xxxxxxx>
---
For example, this ioctl could be used by rust-vmm/rust-kvm or maybe
VirtualBox-kvm in the future.
Documentation/virt/kvm/api.rst | 2 +-
arch/loongarch/kvm/vcpu.c | 69
++++++++++++++++++++++++++++++++++
2 files changed, 70 insertions(+), 1 deletion(-)
diff --git a/Documentation/virt/kvm/api.rst
b/Documentation/virt/kvm/api.rst
index 01a3abef8abb..f46dd8be282f 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -3603,7 +3603,7 @@ VCPU matching underlying host.
---------------------
:Capability: basic
-:Architectures: arm64, mips, riscv, x86 (if KVM_CAP_ONE_REG)
+:Architectures: arm64, loongarch, mips, riscv, x86 (if
KVM_CAP_ONE_REG)
:Type: vcpu ioctl
:Parameters: struct kvm_reg_list (in/out)
:Returns: 0 on success; -1 on error
diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
index 656b954c1134..b884eb9c76aa 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -1186,6 +1186,57 @@ static int kvm_loongarch_vcpu_set_attr(struct
kvm_vcpu *vcpu,
return ret;
}
+static unsigned long kvm_loongarch_num_lbt_regs(void)
+{
+ /* +1 for the LBT_FTOP flag (inside arch.fpu) */
+ return sizeof(struct loongarch_lbt) / sizeof(unsigned long)
+ 1;
+}
+
+static unsigned long kvm_loongarch_num_regs(struct kvm_vcpu *vcpu)
+{
+ /* +1 for the KVM_REG_LOONGARCH_COUNTER register */
+ unsigned long res = CSR_MAX_NUMS + KVM_MAX_CPUCFG_REGS + 1;
+
+ if (kvm_guest_has_lbt(&vcpu->arch))
+ res += kvm_loongarch_num_lbt_regs();
+
+ return res;
+}
+
+static int kvm_loongarch_copy_reg_indices(struct kvm_vcpu *vcpu,
+ u64 __user *uindices)
+{
+ u64 reg;
+ unsigned int i;
+
+ for (i = 0; i < CSR_MAX_NUMS; i++) {
+ reg = KVM_IOC_CSRID(i);
+ if (put_user(reg, uindices++))
+ return -EFAULT;
+ }
part of them is used by vCPU model. By my understanding, there
will be
no much meaning if CSR_MAX_NUMS is returned. And I think it will be
better if real CSR register id and number is returned.
this
function
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/loongarch/kvm/main.c?id=63804fed149a6750ffd28610c5c1c98cce6bd377#n48
?
That looks like a very large list and the values of the register
IDs are
not fully continuous. If that is the case, how do we maintain the
get/set-able CSR register list?
with LoongArch CPU manual CSR register is split into 8 types from
chapter 7.4 -- 7.11
At the beginning, there is big array with size CSR_MAX_NUMS without
any category, it can be fine-gained in late.
Does that mean in the new `kvm_loongarch_copy_reg_indices` function, it
is also okay to embed this big list in there?
actually.
At the second from the word "determine which (special) registers are
get/set-able", I think that it is better to set accessible CSR
register number and ID rather than the total number CSR_MAX_NUMS.
from there to see if I understood your points correctly.
void kvm_init_gcsr_flag(void) {
+ if (cpu_has_msgint) {
+ set_gcsr_hw_flag(LOONGARCH_CSR_ISR0);
+ set_gcsr_hw_flag(LOONGARCH_CSR_ISR1);
+ set_gcsr_hw_flag(LOONGARCH_CSR_ISR2);
+ set_gcsr_hw_flag(LOONGARCH_CSR_ISR3);
+ }
}
Regards
Bibo Mao
+static int kvm_loongarch_num_csr_regs(struct kvm_vcpu *vcpu)Thanks,
+{
+ unsigned int i, count;
+
+ count = 0
+ for (i = 0; i < CSR_MAX_NUMS; i++) {
+ if (!(get_gcsr_flag(i) & (SW_GCSR | HW_GCSR)))
+ continue;
+ count++;
+ }
+ return count;
+}
static unsigned long kvm_loongarch_num_regs(struct kvm_vcpu *vcpu)
{
/* +1 for the KVM_REG_LOONGARCH_COUNTER register */
+ unsigned long res = kvm_loongarch_num_csr_regs +
KVM_MAX_CPUCFG_REGS + 1;
if (kvm_guest_has_lbt(&vcpu->arch))
res += kvm_loongarch_num_lbt_regs();
return res;
}
static int kvm_loongarch_copy_reg_indices(struct kvm_vcpu *vcpu,
u64 __user *uindices)
{
u64 reg;
unsigned int i;
for (i = 0; i < CSR_MAX_NUMS; i++) {
+ if (!(get_gcsr_flag(i) & (SW_GCSR | HW_GCSR)))
+ continue;
reg = KVM_IOC_CSRID(i);
if (put_user(reg, uindices++))
return -EFAULT;
}
Regards
Bibo Mao
Or do you want to extract the list from the `kvm_init_gcsr_flag`
function and refactor both functions to share one single big list
(probably in the kvm_host.h header)?
Because from what I could understand, your previous messages point to
that we need to use this list to make out what CSR registers to return
to the user space VMMs.
Thanks,
Regards
Bibo Mao
RegardsThanks,
Bibo Mao
+
+ for (i = 0; i < KVM_MAX_CPUCFG_REGS; i++) {
+ reg = KVM_IOC_CPUCFG(i);
+ if (put_user(reg, uindices++))
+ return -EFAULT;
+ }
+
+ reg = KVM_REG_LOONGARCH_COUNTER;
+ if (put_user(reg, uindices++))
+ return -EFAULT;
+
+ if (!kvm_guest_has_lbt(&vcpu->arch))
+ return 0;
+
+ for (i = 1; i <= kvm_loongarch_num_lbt_regs(); i++) {
+ reg = (KVM_REG_LOONGARCH_LBT | KVM_REG_SIZE_U64 | i);
+ if (put_user(reg, uindices++))
+ return -EFAULT;
+ }
+
+ return 0;
+}
+
long kvm_arch_vcpu_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
{
@@ -1251,6 +1302,24 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = kvm_loongarch_vcpu_set_attr(vcpu, &attr);
break;
}
+ case KVM_GET_REG_LIST: {
+ struct kvm_reg_list __user *user_list = argp;
+ struct kvm_reg_list reg_list;
+ unsigned n;
+
+ r = -EFAULT;
+ if (copy_from_user(®_list, user_list, sizeof(reg_list)))
+ break;
+ n = reg_list.n;
+ reg_list.n = kvm_loongarch_num_regs(vcpu);
+ if (copy_to_user(user_list, ®_list, sizeof(reg_list)))
+ break;
+ r = -E2BIG;
+ if (n < reg_list.n)
+ break;
+ r = kvm_loongarch_copy_reg_indices(vcpu, user_list->reg);
+ break;
+ }
default:
r = -ENOIOCTLCMD;
break;
Zixing
Zixing
Zixing