lkml.org 
[lkml]   [2022]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v1 2/9] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg
On 30/09/2022 23.07, Janis Schoetterl-Glausch wrote:
> User space can use the MEM_OP ioctl to make storage key checked reads
> and writes to the guest, however, it has no way of performing atomic,
> key checked, accesses to the guest.
> Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg
> mode. For now, support this mode for absolute accesses only.
>
> This mode can be use, for example, to set the device-state-change
> indicator and the adapter-local-summary indicator atomically.
>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
> ---
...
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index eed0315a77a6..b856705f3f6b 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -580,7 +580,9 @@ struct kvm_translation {
> struct kvm_s390_mem_op {
> /* in */
> __u64 gaddr; /* the guest address */
> + /* in & out */
> __u64 flags; /* flags */
> + /* in */
> __u32 size; /* amount of bytes */
> __u32 op; /* type of operation */
> __u64 buf; /* buffer in userspace */
> @@ -588,6 +590,8 @@ struct kvm_s390_mem_op {
> struct {
> __u8 ar; /* the access register number */
> __u8 key; /* access key, ignored if flag unset */
> + /* in & out */
> + __u64 old[2]; /* ignored if flag unset */

The alignment looks very unfortunate now ... could you please add a "__u8
pad[6]" or "__u8 pad[14]" in front of the new field?

> };
> __u32 sida_offset; /* offset into the sida */
> __u8 reserved[32]; /* ignored */
> @@ -604,6 +608,7 @@ struct kvm_s390_mem_op {
> #define KVM_S390_MEMOP_F_CHECK_ONLY (1ULL << 0)
> #define KVM_S390_MEMOP_F_INJECT_EXCEPTION (1ULL << 1)
> #define KVM_S390_MEMOP_F_SKEY_PROTECTION (1ULL << 2)
> +#define KVM_S390_MEMOP_F_CMPXCHG (1ULL << 3)
>
> /* for KVM_INTERRUPT */
> struct kvm_interrupt {
> diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h
> index 9408d6cc8e2c..a1cb66ae0995 100644
> --- a/arch/s390/kvm/gaccess.h
> +++ b/arch/s390/kvm/gaccess.h
> @@ -206,6 +206,10 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
> int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
> void *data, unsigned long len, enum gacc_mode mode);
>
> +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len,
> + unsigned __int128 *old,
> + unsigned __int128 new, u8 access_key);
> +
> /**
> * write_guest_with_key - copy data from kernel space to guest space
> * @vcpu: virtual cpu
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 0243b6e38d36..c0e490ecc372 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -1161,6 +1161,62 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
> return rc;
> }
>
> +/**
> + * cmpxchg_guest_abs_with_key() - Perform cmpxchg on guest absolute address.
> + * @kvm: Virtual machine instance.
> + * @gpa: Absolute guest address of the location to be changed.
> + * @len: Operand length of the cmpxchg, required: 1 <= len <= 16. Providing a
> + * non power of two will result in failure.
> + * @old_p: Pointer to old value. If the location at @gpa contains this value, the
> + * exchange will succeed. After calling cmpxchg_guest_abs_with_key() *@old
> + * contains the value at @gpa before the attempt to exchange the value.
> + * @new: The value to place at @gpa.
> + * @access_key: The access key to use for the guest access.
> + *
> + * Atomically exchange the value at @gpa by @new, if it contains *@old.
> + * Honors storage keys.
> + *
> + * Return: * 0: successful exchange
> + * * 1: exchange unsuccessful
> + * * a program interruption code indicating the reason cmpxchg could
> + * not be attempted
> + * * -EINVAL: address misaligned or len not power of two
> + */
> +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len,
> + unsigned __int128 *old_p, unsigned __int128 new,
> + u8 access_key)
> +{
> + gfn_t gfn = gpa >> PAGE_SHIFT;
> + struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
> + bool writable;
> + hva_t hva;
> + int ret;
> +
> + if (!IS_ALIGNED(gpa, len))
> + return -EINVAL;
> +
> + hva = gfn_to_hva_memslot_prot(slot, gfn, &writable);
> + if (kvm_is_error_hva(hva))
> + return PGM_ADDRESSING;
> + /*
> + * Check if it's a ro memslot, even tho that can't occur (they're unsupported).

Not everybody is used to read such abbreviated English ... I'd recommend to
spell it rather properly (ro ==> read-only, tho ==> though)

> + * Don't try to actually handle that case.
> + */
> + if (!writable)
> + return -EOPNOTSUPP;
> +
> + hva += offset_in_page(gpa);
> + ret = cmpxchg_user_key_size(len, (void __user *)hva, old_p, new, access_key);
> + mark_page_dirty_in_slot(kvm, slot, gfn);
> + /*
> + * Assume that the fault is caused by key protection, the alternative
> + * is that the user page is write protected.
> + */
> + if (ret == -EFAULT)
> + ret = PGM_PROTECTION;
> + return ret;
> +}
> +
> /**
> * guest_translate_address_with_key - translate guest logical into guest absolute address
> * @vcpu: virtual cpu
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index b7ef0b71014d..d594d1318d2a 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -576,7 +576,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_S390_VCPU_RESETS:
> case KVM_CAP_SET_GUEST_DEBUG:
> case KVM_CAP_S390_DIAG318:
> - case KVM_CAP_S390_MEM_OP_EXTENSION:
> r = 1;
> break;
> case KVM_CAP_SET_GUEST_DEBUG2:
> @@ -590,6 +589,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_S390_MEM_OP:
> r = MEM_OP_MAX_SIZE;
> break;
> + case KVM_CAP_S390_MEM_OP_EXTENSION:
> + r = 0x3;

Add a comment to explain that magic value 0x3 ?

> + break;
> case KVM_CAP_NR_VCPUS:
> case KVM_CAP_MAX_VCPUS:
> case KVM_CAP_MAX_VCPU_ID:

Thomas

\
 
 \ /
  Last update: 2022-10-04 10:16    [W:0.118 / U:0.124 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site