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Date: Thu, 23 Sep 2021 14:28:25 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Sohil Mehta <sohil.mehta@...el.com>
Cc: x86@...nel.org, Tony Luck <tony.luck@...el.com>,
Dave Hansen <dave.hansen@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Jens Axboe <axboe@...nel.dk>,
Christian Brauner <christian@...uner.io>,
Peter Zijlstra <peterz@...radead.org>,
Shuah Khan <shuah@...nel.org>, Arnd Bergmann <arnd@...db.de>,
Jonathan Corbet <corbet@....net>,
Ashok Raj <ashok.raj@...el.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
Gayatri Kammela <gayatri.kammela@...el.com>,
Zeng Guang <guang.zeng@...el.com>,
Dan Williams <dan.j.williams@...el.com>,
Randy E Witt <randy.e.witt@...el.com>,
Ravi V Shankar <ravi.v.shankar@...el.com>,
Ramesh Thomas <ramesh.thomas@...el.com>,
linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 10/13] x86/uintr: Introduce user IPI sender syscalls
On Mon, Sep 13, 2021 at 01:01:29PM -0700, Sohil Mehta wrote:
> Add a registration syscall for a task to register itself as a user
> interrupt sender using the uintr_fd generated by the receiver. A task
> can register multiple uintr_fds. Each unique successful connection
> creates a new entry in the User Interrupt Target Table (UITT).
>
> Each entry in the UITT table is referred by the UITT index (uipi_index).
> The uipi_index returned during the registration syscall lets a sender
> generate a user IPI using the 'SENDUIPI <uipi_index>' instruction.
>
> Also, add a sender unregister syscall to unregister a particular task
> from the uintr_fd. Calling close on the uintr_fd will disconnect all
> threads in a sender process from that FD.
>
> Currently, the UITT size is arbitrarily chosen as 256 entries
> corresponding to a 4KB page. Based on feedback and usage data this can
> either be increased/decreased or made dynamic later.
>
> Architecturally, the UITT table can be unique for each thread or shared
> across threads of the same thread group. The current implementation
> keeps the UITT as unique for the each thread. This makes the kernel
> implementation relatively simple and only threads that use uintr get
> setup with the related structures. However, this means that the
> uipi_index for each thread would be inconsistent wrt to other threads.
> (Executing 'SENDUIPI 2' on threads of the same process could generate
> different user interrupts.)
>
> Alternatively, the benefit of sharing the UITT table is that all threads
> would see the same view of the UITT table. Also the kernel UITT memory
> allocation would be more efficient if multiple threads connect to the
> same uintr_fd. However, this would mean the kernel needs to keep the
> UITT table size MISC_MSR[] in sync across these threads. Also the
> UPID/UITT teardown flows might need additional consideration.
>
> Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>
> ---
> arch/x86/include/asm/processor.h | 2 +
> arch/x86/include/asm/uintr.h | 15 ++
> arch/x86/kernel/process.c | 1 +
> arch/x86/kernel/uintr_core.c | 355 ++++++++++++++++++++++++++++++-
> arch/x86/kernel/uintr_fd.c | 133 ++++++++++++
> 5 files changed, 495 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index d229bfac8b4f..3482c3182e39 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -10,6 +10,7 @@ struct mm_struct;
> struct io_bitmap;
> struct vm86;
> struct uintr_receiver;
> +struct uintr_sender;
>
> #include <asm/math_emu.h>
> #include <asm/segment.h>
> @@ -533,6 +534,7 @@ struct thread_struct {
> #ifdef CONFIG_X86_USER_INTERRUPTS
> /* User Interrupt state*/
> struct uintr_receiver *ui_recv;
> + struct uintr_sender *ui_send;
> #endif
>
> /* Floating point and extended processor state */
> diff --git a/arch/x86/include/asm/uintr.h b/arch/x86/include/asm/uintr.h
> index 1f00e2a63da4..ef3521dd7fb9 100644
> --- a/arch/x86/include/asm/uintr.h
> +++ b/arch/x86/include/asm/uintr.h
> @@ -8,6 +8,7 @@ struct uintr_upid_ctx {
> struct task_struct *task; /* Receiver task */
> struct uintr_upid *upid;
> refcount_t refs;
> + bool receiver_active; /* Flag for UPID being mapped to a receiver */
> };
>
> struct uintr_receiver_info {
> @@ -16,12 +17,26 @@ struct uintr_receiver_info {
> u64 uvec; /* Vector number */
> };
>
> +struct uintr_sender_info {
> + struct list_head node;
> + struct uintr_uitt_ctx *uitt_ctx;
> + struct task_struct *task;
> + struct uintr_upid_ctx *r_upid_ctx; /* Receiver's UPID context */
> + struct callback_head twork; /* Task work head */
> + unsigned int uitt_index;
> +};
> +
> bool uintr_arch_enabled(void);
> int do_uintr_register_handler(u64 handler);
> int do_uintr_unregister_handler(void);
> int do_uintr_register_vector(struct uintr_receiver_info *r_info);
> void do_uintr_unregister_vector(struct uintr_receiver_info *r_info);
>
> +int do_uintr_register_sender(struct uintr_receiver_info *r_info,
> + struct uintr_sender_info *s_info);
> +void do_uintr_unregister_sender(struct uintr_receiver_info *r_info,
> + struct uintr_sender_info *s_info);
> +
> void uintr_free(struct task_struct *task);
>
> /* TODO: Inline the context switch related functions */
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 83677f76bd7b..9db33e467b30 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -92,6 +92,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> #ifdef CONFIG_X86_USER_INTERRUPTS
> /* User Interrupt state is unique for each task */
> dst->thread.ui_recv = NULL;
> + dst->thread.ui_send = NULL;
> #endif
>
> return fpu_clone(dst);
> diff --git a/arch/x86/kernel/uintr_core.c b/arch/x86/kernel/uintr_core.c
> index 9dcb9f60e5bc..8f331c5fe0cf 100644
> --- a/arch/x86/kernel/uintr_core.c
> +++ b/arch/x86/kernel/uintr_core.c
> @@ -21,6 +21,11 @@
> #include <asm/msr-index.h>
> #include <asm/uintr.h>
>
> +/*
> + * Each UITT entry is 16 bytes in size.
> + * Current UITT table size is set as 4KB (256 * 16 bytes)
> + */
> +#define UINTR_MAX_UITT_NR 256
> #define UINTR_MAX_UVEC_NR 64
>
> /* User Posted Interrupt Descriptor (UPID) */
> @@ -44,6 +49,27 @@ struct uintr_receiver {
> u64 uvec_mask; /* track active vector per bit */
> };
>
> +/* User Interrupt Target Table Entry (UITTE) */
> +struct uintr_uitt_entry {
> + u8 valid; /* bit 0: valid, bit 1-7: reserved */
Do you check that the other bits are set to 0?
> + u8 user_vec;
> + u8 reserved[6];
What is this reserved for?
> + u64 target_upid_addr;
If this is a pointer, why not say it is a pointer?
> +} __packed __aligned(16);
> +
> +struct uintr_uitt_ctx {
> + struct uintr_uitt_entry *uitt;
> + /* Protect UITT */
> + spinlock_t uitt_lock;
> + refcount_t refs;
Again, a kref please.
thanks,
greg k-h
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