Re: [PATCH v5 06/10] kvm: s390: Add configuration dump functionality

Claudio Imbrenda
2022-05-17T11:37:26Z

On Mon, 16 May 2022 09:08:13 +0000
Janosch Frank <frankja@linux.ibm.com> wrote:

> Sometimes dumping inside of a VM fails, is unavailable or doesn't
> yield the required data. For these occasions we dump the VM from the
> outside, writing memory and cpu data to a file.
>
> Up to now PV guests only supported dumping from the inside of the
> guest through dumpers like KDUMP. A PV guest can be dumped from the
> hypervisor but the data will be stale and / or encrypted.
>
> To get the actual state of the PV VM we need the help of the
> Ultravisor who safeguards the VM state. New UV calls have been added
> to initialize the dump, dump storage state data, dump cpu data and
> complete the dump process. We expose these calls in this patch via a
> new UV ioctl command.
>
> The sensitive parts of the dump data are encrypted, the dump key is
> derived from the Customer Communication Key (CCK). This ensures that
> only the owner of the VM who has the CCK can decrypt the dump data.
>
> The memory is dumped / read via a normal export call and a re-import
> after the dump initialization is not needed (no re-encryption with a
> dump key).
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
> arch/s390/include/asm/kvm_host.h | 1 +
> arch/s390/kvm/kvm-s390.c | 126 +++++++++++++++++++++++++++++++
> arch/s390/kvm/kvm-s390.h | 2 +
> arch/s390/kvm/pv.c | 113 +++++++++++++++++++++++++++
> include/uapi/linux/kvm.h | 15 ++++
> 5 files changed, 257 insertions(+)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 766028d54a3e..a0fbe4820e0a 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -923,6 +923,7 @@ struct kvm_s390_pv {
> u64 guest_len;
> unsigned long stor_base;
> void *stor_var;
> + bool dumping;
> };
>
> struct kvm_arch{
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index de54f14e081e..6bf9dd85d50f 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2271,6 +2271,101 @@ static ssize_t kvm_s390_handle_pv_info(struct kvm_s390_pv_info *info)
> }
> }
>
> +static int kvm_s390_pv_dmp(struct kvm *kvm, struct kvm_pv_cmd *cmd,
> + struct kvm_s390_pv_dmp dmp)
> +{
> + int r = -EINVAL;
> + void __user *result_buff = (void __user *)dmp.buff_addr;
> +
> + switch (dmp.subcmd) {
> + case KVM_PV_DUMP_INIT: {
> + if (kvm->arch.pv.dumping)
> + break;
> +
> + /*
> + * Block SIE entry as concurrent dump UVCs could lead
> + * to validities.

to fatal validity intercepts

> + */
> + kvm_s390_vcpu_block_all(kvm);
> +
> + r = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
> + UVC_CMD_DUMP_INIT, &cmd->rc, &cmd->rrc);
> + KVM_UV_EVENT(kvm, 3, "PROTVIRT DUMP INIT: rc %x rrc %x",
> + cmd->rc, cmd->rrc);
> + if (!r) {
> + kvm->arch.pv.dumping = true;
> + } else {
> + kvm_s390_vcpu_unblock_all(kvm);
> + r = -EINVAL;
> + }
> + break;
> + }
> + case KVM_PV_DUMP_CONFIG_STOR_STATE: {
> + if (!kvm->arch.pv.dumping)
> + break;
> +
> + /*
> + * gaddr is an output parameter since we might stop
> + * early. As dmp will be copied back in our caller, we
> + * don't need to do it ourselves.
> + */
> + r = kvm_s390_pv_dump_stor_state(kvm, result_buff, &dmp.gaddr, dmp.buff_len,
> + &cmd->rc, &cmd->rrc);
> + break;
> + }
> + case KVM_PV_DUMP_COMPLETE: {

this starts to be quite complex, maybe push it into a separate function
as well, like you did for KVM_PV_DUMP_CONFIG_STOR_STATE

> + struct uv_cb_dump_complete complete = {
> + .header.len = sizeof(complete),
> + .header.cmd = UVC_CMD_DUMP_COMPLETE,
> + .config_handle = kvm_s390_pv_get_handle(kvm),
> + };
> + u64 *compl_data;
> +
> + r = -EINVAL;
> + if (!kvm->arch.pv.dumping)
> + break;
> +
> + if (dmp.buff_len < uv_info.conf_dump_finalize_len)
> + break;
> +
> + /* Allocate dump area */
> + r = -ENOMEM;
> + compl_data = vzalloc(uv_info.conf_dump_finalize_len);
> + if (!compl_data)
> + break;
> + complete.dump_area_origin = (u64)compl_data;
> +
> + r = uv_call_sched(0, (u64)&complete);
> + cmd->rc = complete.header.rc;
> + cmd->rrc = complete.header.rrc;
> + KVM_UV_EVENT(kvm, 3, "PROTVIRT DUMP COMPLETE: rc %x rrc %x",
> + complete.header.rc, complete.header.rrc);
> +
> + if (!r) {
> + /*
> + * kvm_s390_pv_dealloc_vm() will also (mem)set
> + * this to false on a reboot or other destroy
> + * operation for this vm.
> + */
> + kvm->arch.pv.dumping = false;
> + kvm_s390_vcpu_unblock_all(kvm);
> + r = copy_to_user(result_buff, compl_data, uv_info.conf_dump_finalize_len);
> + if (r)
> + r = -EFAULT;
> + }
> + vfree(compl_data);
> + if (r > 0)
> + r = -EINVAL;
> + break;
> + }
> + default:
> + r = -ENOTTY;
> + break;
> + }
> +
> + return r;
> +}
> +
> static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
> {
> int r = 0;
> @@ -2447,6 +2542,28 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
> r = 0;
> break;
> }
> + case KVM_PV_DUMP: {
> + struct kvm_s390_pv_dmp dmp;
> +
> + r = -EINVAL;
> + if (!kvm_s390_pv_is_protected(kvm))
> + break;
> +
> + r = -EFAULT;
> + if (copy_from_user(&dmp, argp, sizeof(dmp)))
> + break;
> +
> + r = kvm_s390_pv_dmp(kvm, cmd, dmp);
> + if (r)
> + break;
> +
> + if (copy_to_user(argp, &dmp, sizeof(dmp))) {
> + r = -EFAULT;
> + break;
> + }
> +
> + break;
> + }
> default:
> r = -ENOTTY;
> }
> @@ -4564,6 +4681,15 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
> struct kvm_run *kvm_run = vcpu->run;
> int rc;
>
> + /*
> + * Running a VM while dumping always has the potential to
> + * produce inconsistent dump data. But for PV vcpus a SIE
> + * entry while dumping could also lead to a validity which we

"a fatal validity intercept"

> + * absolutely want to avoid.
> + */
> + if (vcpu->kvm->arch.pv.dumping)
> + return -EINVAL;
> +
> if (kvm_run->immediate_exit)
> return -EINTR;
>
> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
> index 497d52a83c78..2868dd0bba25 100644
> --- a/arch/s390/kvm/kvm-s390.h
> +++ b/arch/s390/kvm/kvm-s390.h
> @@ -250,6 +250,8 @@ int kvm_s390_pv_set_sec_parms(struct kvm *kvm, void *hdr, u64 length, u16 *rc,
> int kvm_s390_pv_unpack(struct kvm *kvm, unsigned long addr, unsigned long size,
> unsigned long tweak, u16 *rc, u16 *rrc);
> int kvm_s390_pv_set_cpu_state(struct kvm_vcpu *vcpu, u8 state);
> +int kvm_s390_pv_dump_stor_state(struct kvm *kvm, void __user *buff_user,
> + u64 *gaddr, u64 buff_user_len, u16 *rc, u16 *rrc);
>
> static inline u64 kvm_s390_pv_get_handle(struct kvm *kvm)
> {
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index cc7c9599f43e..fd261667d2c2 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -7,6 +7,7 @@
> */
> #include <linux/kvm.h>
> #include <linux/kvm_host.h>
> +#include <linux/minmax.h>
> #include <linux/pagemap.h>
> #include <linux/sched/signal.h>
> #include <asm/gmap.h>
> @@ -298,3 +299,115 @@ int kvm_s390_pv_set_cpu_state(struct kvm_vcpu *vcpu, u8 state)
> return -EINVAL;
> return 0;
> }
> +
> +/* Size of the cache for the storage state dump data. 1MB for now */
> +#define DUMP_BUFF_LEN HPAGE_SIZE
> +
> +/*
> + * kvm_s390_pv_dump_stor_state
> + *
> + * @kvm: pointer to the guest's KVM struct
> + * @buff_user: Userspace pointer where we will write the results to
> + * @gaddr: Starting absolute guest address for which the storage state
> + * is requested. This value will be updated with the last
> + * address for which data was written when returning to
> + * userspace.
> + * @buff_user_len: Length of the buff_user buffer
> + * @rc: Pointer to where the uvcb return code is stored
> + * @rrc: Pointer to where the uvcb return reason code is stored
> + *

please add:
Context: kvm->lock needs to be held

also explain that part of the user buffer might be written to even in
case of failure (this also needs to go in the documentation)

> + * Return:
> + * 0 on success

rc and rrc will also be set in case of success

> + * -ENOMEM if allocating the cache fails
> + * -EINVAL if gaddr is not aligned to 1MB
> + * -EINVAL if buff_user_len is not aligned to uv_info.conf_dump_storage_state_len
> + * -EINVAL if the UV call fails, rc and rrc will be set in this case

have you considered a different code for UVC failure?
so the caller can know that rc and rrc are meaningful

or just explain that rc and rrc will always be set; if the UVC is not
performed, rc and rrc will be 0

> + * -EFAULT if copying the result to buff_user failed
> + */
> +int kvm_s390_pv_dump_stor_state(struct kvm *kvm, void __user *buff_user,
> + u64 *gaddr, u64 buff_user_len, u16 *rc, u16 *rrc)
> +{
> + struct uv_cb_dump_stor_state uvcb = {
> + .header.cmd = UVC_CMD_DUMP_CONF_STOR_STATE,
> + .header.len = sizeof(uvcb),
> + .config_handle = kvm->arch.pv.handle,
> + .gaddr = *gaddr,
> + .dump_area_origin = 0,
> + };
> + size_t buff_kvm_size;
> + size_t size_done = 0;
> + u8 *buff_kvm = NULL;
> + int cc, ret;
> +
> + ret = -EINVAL;
> + /* UV call processes 1MB guest storage chunks at a time */
> + if (!IS_ALIGNED(*gaddr, HPAGE_SIZE))
> + goto out;
> +
> + /*
> + * We provide the storage state for 1MB chunks of guest
> + * storage. The buffer will need to be aligned to
> + * conf_dump_storage_state_len so we don't end on a partial
> + * chunk.
> + */
> + if (!buff_user_len ||
> + !IS_ALIGNED(buff_user_len, uv_info.conf_dump_storage_state_len))
> + goto out;
> +
> + /*
> + * Allocate a buffer from which we will later copy to the user
> + * process. We don't want userspace to dictate our buffer size
> + * so we limit it to DUMP_BUFF_LEN.
> + */
> + ret = -ENOMEM;
> + buff_kvm_size = min_t(u64, buff_user_len, DUMP_BUFF_LEN);
> + buff_kvm = vzalloc(buff_kvm_size);
> + if (!buff_kvm)
> + goto out;
> +
> + ret = 0;
> + uvcb.dump_area_origin = (u64)buff_kvm;
> + /* We will loop until the user buffer is filled or an error occurs */
> + do {
> + /* Get 1MB worth of guest storage state data */
> + cc = uv_call_sched(0, (u64)&uvcb);
> +
> + /* All or nothing */
> + if (cc) {
> + ret = -EINVAL;
> + break;
> + }
> +
> + size_done += uv_info.conf_dump_storage_state_len;

maybe save this in a local const variable with a shorter name? would be
more readable? const u64 dump_len = uv_info.conf_dump_storage_state_len;

> + uvcb.dump_area_origin += uv_info.conf_dump_storage_state_len;
> + buff_user_len -= uv_info.conf_dump_storage_state_len;
> + uvcb.gaddr += HPAGE_SIZE;
> +
> + /* KVM Buffer full, time to copy to the process */
> + if (!buff_user_len || size_done == DUMP_BUFF_LEN) {
> + if (copy_to_user(buff_user, buff_kvm, size_done)) {
> + ret = -EFAULT;
> + break;
> + }
> +
> + buff_user += size_done;
> + size_done = 0;
> + uvcb.dump_area_origin = (u64)buff_kvm;
> + }
> + } while (buff_user_len);
> +
> + /* Report back where we ended dumping */
> + *gaddr = uvcb.gaddr;
> +
> + /* Lets only log errors, we don't want to spam */
> +out:
> + if (ret)
> + KVM_UV_EVENT(kvm, 3,
> + "PROTVIRT DUMP STORAGE STATE: addr %llx ret %d, uvcb rc %x rrc %x",
> + uvcb.gaddr, ret, uvcb.header.rc, uvcb.header.rrc);
> + *rc = uvcb.header.rc;
> + *rrc = uvcb.header.rrc;
> + vfree(buff_kvm);
> +
> + return ret;
> +}
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index bb2f91bc2305..1c60c2d314ba 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1653,6 +1653,20 @@ struct kvm_s390_pv_unp {
> __u64 tweak;
> };
>
> +enum pv_cmd_dmp_id {
> + KVM_PV_DUMP_INIT,
> + KVM_PV_DUMP_CONFIG_STOR_STATE,
> + KVM_PV_DUMP_COMPLETE,
> +};
> +
> +struct kvm_s390_pv_dmp {
> + __u64 subcmd;
> + __u64 buff_addr;
> + __u64 buff_len;
> + __u64 gaddr; /* For dump storage state */
> + __u64 reserved[4];
> +};
> +
> enum pv_cmd_info_id {
> KVM_PV_INFO_VM,
> KVM_PV_INFO_DUMP,
> @@ -1696,6 +1710,7 @@ enum pv_cmd_id {
> KVM_PV_PREP_RESET,
> KVM_PV_UNSHARE_ALL,
> KVM_PV_INFO,
> + KVM_PV_DUMP,
> };
>
> struct kvm_pv_cmd {