Re: [RFC PATCH 04/13] x86/fpu/xstate: Enumerate User Interrupts supervisor state

[Sohil Mehta]

On 9/23/2021 3:34 PM, Thomas Gleixner wrote:
> On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:
> > Enable xstate supervisor support for User Interrupts by default.
> What means enabled by default? It's enabled when available and not
> disabled on the command line.

I'll remove it.

> > The user interrupt state for a task consists of the MSR state and the
> > User Interrupt Flag (UIF) value. XSAVES and XRSTORS handle saving and
> > restoring both of these states.
> >
> > <The supervisor XSTATE code might be reworked based on issues reported
> > in the past. The Uintr context switching code would also need rework and
> > additional testing in that regard.>
> What? Which issues were reported and if they have been reported then how
> is the provided code correct?


I apologize for causing this confusion. This comment was added a few 
months back when the PKRU and FPU code was being reworked. This comment 
is no longer valid.

> > +/*
> > + * State component 14 is supervisor state used for User Interrupts state.
> > + * The size of this state is 48 bytes
> > + */
> > +struct uintr_state {
> > +	u64 handler;
> > +	u64 stack_adjust;
> > +	u32 uitt_size;
> > +	u8  uinv;
> > +	u8  pad1;
> > +	u8  pad2;
> > +	u8  uif_pad3;		/* bit 7 - UIF, bits 6:0 - reserved */
> Please do not use tail comments. Also what kind of name is uif_pad3?
> Bitfields exist for a reason.


An internal version of this used bitfields. I was suggested that use of 
bitfields is not recommended for x86 code.

The name uif_pad3 is really ugly though. I'll change it to a bitfield 
next time.


Thanks,

Sohil