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Message-ID: <87czoyg88k.ffs@tglx>
Date: Fri, 24 Sep 2021 01:52:43 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Sohil Mehta <sohil.mehta@...el.com>, x86@...nel.org
Cc: Sohil Mehta <sohil.mehta@...el.com>,
Tony Luck <tony.luck@...el.com>,
Dave Hansen <dave.hansen@...el.com>,
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 06/13] x86/uintr: Introduce uintr receiver syscalls
On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:
> +/* User Posted Interrupt Descriptor (UPID) */
> +struct uintr_upid {
> + struct {
> + u8 status; /* bit 0: ON, bit 1: SN, bit 2-7: reserved */
> + u8 reserved1; /* Reserved */
> + u8 nv; /* Notification vector */
> + u8 reserved2; /* Reserved */
> + u32 ndst; /* Notification destination */
> + } nc __packed; /* Notification control */
> + u64 puir; /* Posted user interrupt requests */
> +} __aligned(64);
> +
> +/* UPID Notification control status */
> +#define UPID_ON 0x0 /* Outstanding notification */
> +#define UPID_SN 0x1 /* Suppressed notification */
Come on. This are bits in upid.status, right? So why can't the comment
above these defines says so and why can't the names not reflect that?
> +struct uintr_upid_ctx {
> + struct uintr_upid *upid;
> + refcount_t refs;
Please use tabular format for struct members.
> +};
> +
> +struct uintr_receiver {
> + struct uintr_upid_ctx *upid_ctx;
> +};
So we need a struct to wrap a pointer to another struct. Why?
> +inline bool uintr_arch_enabled(void)
What's this arch_enabled indirection for? Is this used anywhere in
non-architecture code?
> +{
> + return static_cpu_has(X86_FEATURE_UINTR);
> +}
> +
> +static inline bool is_uintr_receiver(struct task_struct *t)
> +{
> + return !!t->thread.ui_recv;
> +}
> +
> +static inline u32 cpu_to_ndst(int cpu)
> +{
> + u32 apicid = (u32)apic->cpu_present_to_apicid(cpu);
> +
> + WARN_ON_ONCE(apicid == BAD_APICID);
Brilliant. If x2apic is not enabled then this case returns
> + if (!x2apic_enabled())
> + return (apicid << 8) & 0xFF00;
(BAD_APICID << 8) & 0xFF00 == 0xFF ....
> +int do_uintr_unregister_handler(void)
> +{
> + struct task_struct *t = current;
> + struct fpu *fpu = &t->thread.fpu;
> + struct uintr_receiver *ui_recv;
> + u64 msr64;
> +
> + if (!is_uintr_receiver(t))
> + return -EINVAL;
> +
> + pr_debug("recv: Unregister handler and clear MSRs for task=%d\n",
> + t->pid);
> +
> + /*
> + * TODO: Evaluate usage of fpregs_lock() and get_xsave_addr(). Bugs
> + * have been reported recently for PASID and WRPKRU.
Again. Which bugs and why haven't they been evaluated before posting?
> + * UPID and ui_recv will be referenced during context switch. Need to
> + * disable preemption while modifying the MSRs, UPID and ui_recv thread
> + * struct.
> + */
> + fpregs_lock();
And because you need to disable preemption you need to use
fpregs_lock(), right? That's not what fpregs_lock() is about.
> + /* Clear only the receiver specific state. Sender related state is not modified */
> + if (fpregs_state_valid(fpu, smp_processor_id())) {
> + /* Modify only the relevant bits of the MISC MSR */
> + rdmsrl(MSR_IA32_UINTR_MISC, msr64);
> + msr64 &= ~GENMASK_ULL(39, 32);
This is exactly the crap which results from not defining stuff
properly. Random numbers in code which nobody can understand.
> + wrmsrl(MSR_IA32_UINTR_MISC, msr64);
> + wrmsrl(MSR_IA32_UINTR_PD, 0ULL);
> + wrmsrl(MSR_IA32_UINTR_RR, 0ULL);
> + wrmsrl(MSR_IA32_UINTR_STACKADJUST, 0ULL);
> + wrmsrl(MSR_IA32_UINTR_HANDLER, 0ULL);
> + } else {
> + struct uintr_state *p;
> +
> + p = get_xsave_addr(&fpu->state.xsave, XFEATURE_UINTR);
> + if (p) {
> + p->handler = 0;
> + p->stack_adjust = 0;
> + p->upid_addr = 0;
> + p->uinv = 0;
> + p->uirr = 0;
> + }
So p == NULL is expected here?
> + }
> +
> + ui_recv = t->thread.ui_recv;
> + /*
> + * Suppress notifications so that no further interrupts are generated
> + * based on this UPID.
> + */
> + set_bit(UPID_SN, (unsigned long *)&ui_recv->upid_ctx->upid->nc.status);
> +
> + put_upid_ref(ui_recv->upid_ctx);
> + kfree(ui_recv);
> + t->thread.ui_recv = NULL;
Why has this put/kfree stuff to be in the fpregs locked section?
> + fpregs_unlock();
> +
> + return 0;
> +}
> +
> +int do_uintr_register_handler(u64 handler)
> +{
> + struct uintr_receiver *ui_recv;
> + struct uintr_upid *upid;
> + struct task_struct *t = current;
> + struct fpu *fpu = &t->thread.fpu;
> + u64 misc_msr;
> + int cpu;
> +
> + if (is_uintr_receiver(t))
> + return -EBUSY;
> +
> + ui_recv = kzalloc(sizeof(*ui_recv), GFP_KERNEL);
> + if (!ui_recv)
> + return -ENOMEM;
> +
> + ui_recv->upid_ctx = alloc_upid();
> + if (!ui_recv->upid_ctx) {
> + kfree(ui_recv);
> + pr_debug("recv: alloc upid failed for task=%d\n", t->pid);
> + return -ENOMEM;
> + }
> +
> + /*
> + * TODO: Evaluate usage of fpregs_lock() and get_xsave_addr(). Bugs
> + * have been reported recently for PASID and WRPKRU.
Oh well.
> + * UPID and ui_recv will be referenced during context switch. Need to
> + * disable preemption while modifying the MSRs, UPID and ui_recv thread
> + * struct.
See above.
> + */
> + fpregs_lock();
> +
> + cpu = smp_processor_id();
> + upid = ui_recv->upid_ctx->upid;
> + upid->nc.nv = UINTR_NOTIFICATION_VECTOR;
> + upid->nc.ndst = cpu_to_ndst(cpu);
> +
> + t->thread.ui_recv = ui_recv;
> +
> + if (fpregs_state_valid(fpu, cpu)) {
> + wrmsrl(MSR_IA32_UINTR_HANDLER, handler);
> + wrmsrl(MSR_IA32_UINTR_PD, (u64)ui_recv->upid_ctx->upid);
> +
> + /* Set value as size of ABI redzone */
> + wrmsrl(MSR_IA32_UINTR_STACKADJUST, 128);
> +
> + /* Modify only the relevant bits of the MISC MSR */
> + rdmsrl(MSR_IA32_UINTR_MISC, misc_msr);
> + misc_msr |= (u64)UINTR_NOTIFICATION_VECTOR << 32;
> + wrmsrl(MSR_IA32_UINTR_MISC, misc_msr);
> + } else {
> + struct xregs_state *xsave;
> + struct uintr_state *p;
> +
> + xsave = &fpu->state.xsave;
> + xsave->header.xfeatures |= XFEATURE_MASK_UINTR;
> + p = get_xsave_addr(&fpu->state.xsave, XFEATURE_UINTR);
> + if (p) {
> + p->handler = handler;
> + p->upid_addr = (u64)ui_recv->upid_ctx->upid;
> + p->stack_adjust = 128;
> + p->uinv = UINTR_NOTIFICATION_VECTOR;
> + }
Again. How is p supposed to be NULL and if so, why is this silently
treating this as success?
> + }
> +
> + fpregs_unlock();
Thanks,
tglx
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