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SubjectRE: [RFC PATCH 16/18] virt/mshv: mmap vp register page
Date
From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Friday, November 20, 2020 4:31 PM
>
> Introduce mmap interface for a virtual processor, exposing a page for
> setting and getting common registers while the VP is suspended.
>
> This provides a more performant and convenient way to get and set these
> registers in the context of a vmm's run-loop.
>
> Co-developed-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> Signed-off-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> ---
> Documentation/virt/mshv/api.rst | 11 ++++
> arch/x86/include/uapi/asm/hyperv-tlfs.h | 74 ++++++++++++++++++++++
> include/asm-generic/hyperv-tlfs.h | 10 +++
> include/linux/mshv.h | 1 +
> include/uapi/asm-generic/hyperv-tlfs.h | 5 ++
> include/uapi/linux/mshv.h | 12 ++++
> virt/mshv/mshv_main.c | 82 +++++++++++++++++++++++++
> 7 files changed, 195 insertions(+)
>
> diff --git a/Documentation/virt/mshv/api.rst b/Documentation/virt/mshv/api.rst
> index 7fd75f248eff..89c276a8778f 100644
> --- a/Documentation/virt/mshv/api.rst
> +++ b/Documentation/virt/mshv/api.rst
> @@ -149,3 +149,14 @@ HV_PARTITION_CREATION_FLAG_LAPIC_ENABLED
> Get/set various vp state. Currently these can be used to get and set
> emulated LAPIC state, and xsave data.
>
> +3.10 mmap(vp)
> +-------------
> +:Type: vp mmap
> +:Parameters: offset should be HV_VP_MMAP_REGISTERS_OFFSET
> +:Returns: 0 on success
> +
> +Maps a page into userspace that can be used to get and set common registers
> +while the vp is suspended.
> +The page is laid out in struct hv_vp_register_page in asm/hyperv-tlfs.h.
> +

I'm assuming there's no support for the corresponding munmap().
What happens if munmap is called? Does it just fail and the page remains
mapped?

> +
> diff --git a/arch/x86/include/uapi/asm/hyperv-tlfs.h b/arch/x86/include/uapi/asm/hyperv-
> tlfs.h
> index 78758aedf23e..a241178567ff 100644
> --- a/arch/x86/include/uapi/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/uapi/asm/hyperv-tlfs.h
> @@ -1110,4 +1110,78 @@ struct hv_vp_state_data_xsave {
> union hv_x64_xsave_xfem_register states;
> };
>
> +/* Bits for dirty mask of hv_vp_register_page */
> +#define HV_X64_REGISTER_CLASS_GENERAL 0
> +#define HV_X64_REGISTER_CLASS_IP 1
> +#define HV_X64_REGISTER_CLASS_XMM 2
> +#define HV_X64_REGISTER_CLASS_SEGMENT 3
> +#define HV_X64_REGISTER_CLASS_FLAGS 4
> +
> +#define HV_VP_REGISTER_PAGE_VERSION_1 1u
> +
> +struct hv_vp_register_page {
> + __u16 version;
> + bool isvalid;

Like enum, avoid type "bool" in data structures shared with
Hyper-V.

> + __u8 rsvdz;
> + __u32 dirty;
> + union {
> + struct {
> + __u64 rax;
> + __u64 rcx;
> + __u64 rdx;
> + __u64 rbx;
> + __u64 rsp;
> + __u64 rbp;
> + __u64 rsi;
> + __u64 rdi;
> + __u64 r8;
> + __u64 r9;
> + __u64 r10;
> + __u64 r11;
> + __u64 r12;
> + __u64 r13;
> + __u64 r14;
> + __u64 r15;
> + };
> +
> + __u64 gp_registers[16];
> + };
> + __u64 rip;
> + __u64 rflags;
> + union {
> + struct {
> + struct hv_u128 xmm0;
> + struct hv_u128 xmm1;
> + struct hv_u128 xmm2;
> + struct hv_u128 xmm3;
> + struct hv_u128 xmm4;
> + struct hv_u128 xmm5;
> + };
> +
> + struct hv_u128 xmm_registers[6];
> + };
> + union {
> + struct {
> + struct hv_x64_segment_register es;
> + struct hv_x64_segment_register cs;
> + struct hv_x64_segment_register ss;
> + struct hv_x64_segment_register ds;
> + struct hv_x64_segment_register fs;
> + struct hv_x64_segment_register gs;
> + };
> +
> + struct hv_x64_segment_register segment_registers[6];
> + };
> + /* read only */
> + __u64 cr0;
> + __u64 cr3;
> + __u64 cr4;
> + __u64 cr8;
> + __u64 efer;
> + __u64 dr7;
> + union hv_x64_pending_interruption_register pending_interruption;
> + union hv_x64_interrupt_state_register interrupt_state;
> + __u64 instruction_emulation_hints;
> +};
> +
> #endif
> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index 4bc59a0344ce..9eed4b869110 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -837,4 +837,14 @@ struct hv_set_vp_state_in {
> union hv_input_set_vp_state_data data[];
> };
>
> +struct hv_map_vp_state_page_in {
> + u64 partition_id;
> + u32 vp_index;
> + enum hv_vp_state_page_type type;
> +};
> +
> +struct hv_map_vp_state_page_out {
> + u64 map_location; /* page number */
> +};
> +
> #endif
> diff --git a/include/linux/mshv.h b/include/linux/mshv.h
> index 3933d80294f1..33f4d0cfee11 100644
> --- a/include/linux/mshv.h
> +++ b/include/linux/mshv.h
> @@ -20,6 +20,7 @@ struct mshv_vp {
> u32 index;
> struct mshv_partition *partition;
> struct mutex mutex;
> + struct page *register_page;
> struct {
> struct semaphore sem;
> struct task_struct *task;
> diff --git a/include/uapi/asm-generic/hyperv-tlfs.h b/include/uapi/asm-generic/hyperv-
> tlfs.h
> index b3c84c69b73f..a747f39b132a 100644
> --- a/include/uapi/asm-generic/hyperv-tlfs.h
> +++ b/include/uapi/asm-generic/hyperv-tlfs.h
> @@ -92,4 +92,9 @@ enum hv_get_set_vp_state_type {
> HV_GET_SET_VP_STATE_SYNTHETIC_TIMERS = 4,
> };
>
> +enum hv_vp_state_page_type {
> + HV_VP_STATE_PAGE_REGISTERS = 0,
> + HV_VP_STATE_PAGE_COUNT
> +};
> +
> #endif
> diff --git a/include/uapi/linux/mshv.h b/include/uapi/linux/mshv.h
> index ae0bb64bbec3..8537ff29aee5 100644
> --- a/include/uapi/linux/mshv.h
> +++ b/include/uapi/linux/mshv.h
> @@ -13,6 +13,8 @@
>
> #define MSHV_VERSION 0x0
>
> +#define MSHV_VP_MMAP_REGISTERS_OFFSET (HV_VP_STATE_PAGE_REGISTERS * 0x1000)
> +
> struct mshv_create_partition {
> __u64 flags;
> struct hv_partition_creation_properties partition_creation_properties;
> @@ -84,4 +86,14 @@ struct mshv_vp_state {
> #define MSHV_GET_VP_STATE _IOWR(MSHV_IOCTL, 0x0A, struct mshv_vp_state)
> #define MSHV_SET_VP_STATE _IOWR(MSHV_IOCTL, 0x0B, struct mshv_vp_state)
>
> +/* register page mapping example:
> + * struct hv_vp_register_page *regs = mmap(NULL,
> + * 4096,
> + * PROT_READ | PROT_WRITE,
> + * MAP_SHARED,
> + * vp_fd,
> + * HV_VP_MMAP_REGISTERS_OFFSET);
> + * munmap(regs, 4096);
> + */
> +
> #endif
> diff --git a/virt/mshv/mshv_main.c b/virt/mshv/mshv_main.c
> index 70172d9488de..a597254fa4f4 100644
> --- a/virt/mshv/mshv_main.c
> +++ b/virt/mshv/mshv_main.c
> @@ -43,11 +43,18 @@ static long mshv_partition_ioctl(struct file *filp, unsigned int ioctl,
> unsigned
> static int mshv_dev_open(struct inode *inode, struct file *filp);
> static int mshv_dev_release(struct inode *inode, struct file *filp);
> static long mshv_dev_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg);
> +static int mshv_vp_mmap(struct file *file, struct vm_area_struct *vma);
> +static vm_fault_t mshv_vp_fault(struct vm_fault *vmf);
> +
> +static const struct vm_operations_struct mshv_vp_vm_ops = {
> + .fault = mshv_vp_fault,
> +};
>
> static const struct file_operations mshv_vp_fops = {
> .release = mshv_vp_release,
> .unlocked_ioctl = mshv_vp_ioctl,
> .llseek = noop_llseek,
> + .mmap = mshv_vp_mmap,
> };
>
> static const struct file_operations mshv_partition_fops = {
> @@ -499,6 +506,47 @@ hv_call_set_vp_registers(u32 vp_index,
> return -hv_status_to_errno(status);
> }
>
> +static int
> +hv_call_map_vp_state_page(u32 vp_index, u64 partition_id,
> + struct page **state_page)
> +{
> + struct hv_map_vp_state_page_in *input;
> + struct hv_map_vp_state_page_out *output;
> + int status;
> + int ret;
> + unsigned long flags;
> +
> + do {
> + local_irq_save(flags);
> + input = (struct hv_map_vp_state_page_in *)(*this_cpu_ptr(
> + hyperv_pcpu_input_arg));
> + output = (struct hv_map_vp_state_page_out *)(*this_cpu_ptr(
> + hyperv_pcpu_output_arg));
> +
> + input->partition_id = partition_id;
> + input->vp_index = vp_index;
> + input->type = HV_VP_STATE_PAGE_REGISTERS;
> + status = hv_do_hypercall(HVCALL_MAP_VP_STATE_PAGE,
> + input, output);
> +
> + if (status != HV_STATUS_INSUFFICIENT_MEMORY) {
> + if (status == HV_STATUS_SUCCESS)
> + *state_page = pfn_to_page(output->map_location);
> + else
> + pr_err("%s: %s\n", __func__,
> + hv_status_to_string(status));
> + local_irq_restore(flags);
> + ret = -hv_status_to_errno(status);
> + break;
> + }
> + local_irq_restore(flags);
> +
> + ret = hv_call_deposit_pages(NUMA_NO_NODE, partition_id, 1);
> + } while (!ret);
> +
> + return ret;
> +}
> +
> static void
> mshv_isr(void)
> {
> @@ -1155,6 +1203,40 @@ mshv_vp_ioctl(struct file *filp, unsigned int ioctl, unsigned long
> arg)
> return r;
> }
>
> +static vm_fault_t mshv_vp_fault(struct vm_fault *vmf)
> +{
> + struct mshv_vp *vp = vmf->vma->vm_file->private_data;
> +
> + vmf->page = vp->register_page;
> +
> + return 0;
> +}
> +
> +static int mshv_vp_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + int ret;
> + struct mshv_vp *vp = file->private_data;
> +
> + if (vma->vm_pgoff != MSHV_VP_MMAP_REGISTERS_OFFSET)
> + return -EINVAL;
> +
> + if (mutex_lock_killable(&vp->mutex))
> + return -EINTR;
> +
> + if (!vp->register_page) {
> + ret = hv_call_map_vp_state_page(vp->index,
> + vp->partition->id,
> + &vp->register_page);
> + if (ret)
> + return ret;
> + }
> +
> + mutex_unlock(&vp->mutex);
> +
> + vma->vm_ops = &mshv_vp_vm_ops;
> + return 0;
> +}
> +
> static int
> mshv_vp_release(struct inode *inode, struct file *filp)
> {
> --
> 2.25.1

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