linux-kernel - Re: [PATCH RFC 01/13] x86: Move posted interrupt descriptor out of vmx code

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Date:   Thu, 7 Dec 2023 20:54:31 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.org>,
        iommu@...ts.linux.dev, Lu Baolu <baolu.lu@...ux.intel.com>,
        kvm@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...hat.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, maz@...nel.org,
        peterz@...radead.org, seanjc@...gle.com,
        Robin Murphy <robin.murphy@....com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH RFC 01/13] x86: Move posted interrupt descriptor out of
 vmx code

Hi Thomas,

On Wed, 06 Dec 2023 17:33:28 +0100, Thomas Gleixner <tglx@...utronix.de>
wrote:

> On Sat, Nov 11 2023 at 20:16, Jacob Pan wrote:
> > +/* Posted-Interrupt Descriptor */
> > +struct pi_desc {
> > +	u32 pir[8];     /* Posted interrupt requested */
> > +	union {
> > +		struct {
> > +				/* bit 256 - Outstanding Notification
> > */
> > +			u16	on	: 1,
> > +				/* bit 257 - Suppress Notification */
> > +				sn	: 1,
> > +				/* bit 271:258 - Reserved */
> > +				rsvd_1	: 14;
> > +				/* bit 279:272 - Notification Vector */
> > +			u8	nv;
> > +				/* bit 287:280 - Reserved */
> > +			u8	rsvd_2;
> > +				/* bit 319:288 - Notification
> > Destination */
> > +			u32	ndst;  
> 
> This mixture of bitfields and types is weird and really not intuitive:
> 
> /* Posted-Interrupt Descriptor */
> struct pi_desc {
> 	/* Posted interrupt requested */
> 	u32			pir[8];
> 
> 	union {
> 		struct {
> 				/* bit 256 - Outstanding Notification */
> 			u64	on	:  1,
> 				/* bit 257 - Suppress Notification */
> 				sn	:  1,
> 				/* bit 271:258 - Reserved */
> 					: 14,
> 				/* bit 279:272 - Notification Vector */
> 				nv	:  8,
> 				/* bit 287:280 - Reserved */
> 					:  8,
> 				/* bit 319:288 - Notification Destination
> */ ndst	: 32;
> 		};
> 		u64		control;
> 	};
> 	u32			rsvd[6];
> } __aligned(64);
> 
It seems bit-fields cannot pass type check. I got these compile error.

arch/x86/kernel/irq.c: In function ‘intel_posted_msi_init’:
./include/linux/percpu-defs.h:363:20: error: cannot take address of bit-field ‘nv’
  363 |  __verify_pcpu_ptr(&(variable));     \
      |                    ^
./include/linux/percpu-defs.h:219:47: note: in definition of macro ‘__verify_pcpu_ptr’
  219 |  const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL; \
      |                                               ^~~
./include/linux/percpu-defs.h:490:34: note: in expansion of macro ‘__pcpu_size_call’
  490 | #define this_cpu_write(pcp, val) __pcpu_size_call(this_cpu_write_, pcp, val)
      |                                  ^~~~~~~~~~~~~~~~
arch/x86/kernel/irq.c:358:2: note: in expansion of macro ‘this_cpu_write’
  358 |  this_cpu_write(posted_interrupt_desc.nv, POSTED_MSI_NOTIFICATION_VECTOR);
      |  ^~~~~~~~~~~~~~
./include/linux/percpu-defs.h:364:15: error: ‘sizeof’ applied to a bit-field
  364 |  switch(sizeof(variable)) {     \
> 
> > +static inline bool pi_test_and_set_on(struct pi_desc *pi_desc)
> > +{
> > +	return test_and_set_bit(POSTED_INTR_ON,
> > +			(unsigned long *)&pi_desc->control);  
> 
> Please get rid of those line breaks.
will do.


Thanks,

Jacob