| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <13746394-1a33-894a-d325-8125743f7906@loongson.cn>
Date: Mon, 26 Jan 2026 16:36:57 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: liushuyu <liushuyu@...c.io>, WANG Xuerui <kernel@...0n.name>,
Huacai Chen <chenhuacai@...nel.org>
Cc: Kexy Biscuit <kexybiscuit@...c.io>, Mingcong Bai <jeffbai@...c.io>,
Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
Tianrui Zhao <zhaotianrui@...ngson.cn>, Paul Walmsley <pjw@...nel.org>,
Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
Alexandre Ghiti <alex@...ti.fr>, Miguel Ojeda <ojeda@...nel.org>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>, kvm@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
loongarch@...ts.linux.dev, linux-riscv@...ts.infradead.org,
rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/1] KVM: Add KVM_GET_REG_LIST ioctl for LoongArch
On 2026/1/26 下午12:22, liushuyu wrote:
> Hi Bibo,
>
>>
>>
>> On 2026/1/26 上午11:38, liushuyu wrote:
>>> Hi Bibo,
>>>>
>>>>
>>>> On 2026/1/25 下午1:43, Zixing Liu wrote:
>>>>> This ioctl can be used by userspace applications to determine which
>>>>> (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@...c.io>
>>>>> ---
>>>>>
>>>>> 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;
>>>>> + }
>>>> CSR_MAX_NUMS is max number of accessible CSR registers, instead only
>>>> 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.
>>>>
>>> Did you mean we should only return the CSR registers initialized in 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?
>> It will be better if CSR register list can be categorized, for example
>> 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?
Firstly I do not know how to use ioctl command KVM_GET_REG_LIST in VMM
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.
+static int kvm_loongarch_num_csr_regs(struct kvm_vcpu *vcpu)
+{
+ 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.
>
>>
>> Regards
>> Bibo Mao
>>>
>>>> Regards
>>>> 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;
>>>>>
>>>>
>>> Thanks,
>>> Zixing
>>>
>>
> Thanks,
> Zixing
>
Powered by blists - more mailing lists