Re: [Xen-devel] [PATCH v5 09/11] viridian: add implementation of synthetic interrupt MSRs

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Jan Beulich
> Sent: 13 March 2019 13:15
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu 
> <wei.liu2@xxxxxxxxxx>; Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>; Andrew 
> Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Tim 
> (Xen.org) <tim@xxxxxxx>; Julien
> Grall <julien.grall@xxxxxxx>; xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>; 
> Roger Pau Monne
> <roger.pau@xxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v5 09/11] viridian: add implementation of 
> synthetic interrupt MSRs
> 
> >>> On 11.03.19 at 14:41, <paul.durrant@xxxxxxxxxx> wrote:
> > @@ -28,6 +29,32 @@ typedef union _HV_VP_ASSIST_PAGE
> >      uint8_t ReservedZBytePadding[PAGE_SIZE];
> >  } HV_VP_ASSIST_PAGE;
> >
> > +typedef enum HV_MESSAGE_TYPE {
> > +    HvMessageTypeNone,
> > +    HvMessageTimerExpired = 0x80000010,
> > +} HV_MESSAGE_TYPE;
> > +
> > +typedef struct HV_MESSAGE_FLAGS {
> > +    uint8_t MessagePending:1;
> > +    uint8_t Reserved:7;
> > +} HV_MESSAGE_FLAGS;
> > +
> > +typedef struct HV_MESSAGE_HEADER {
> > +    HV_MESSAGE_TYPE MessageType;
> > +    uint16_t Reserved1;
> > +    HV_MESSAGE_FLAGS MessageFlags;
> > +    uint8_t PayloadSize;
> > +    uint64_t Reserved2;
> > +} HV_MESSAGE_HEADER;
> > +
> > +#define HV_MESSAGE_SIZE 256
> > +#define HV_MESSAGE_MAX_PAYLOAD_QWORD_COUNT 30
> 

Missed this one before...

> Is this defined this way, or (given ...
> 
> > +typedef struct HV_MESSAGE {
> > +    HV_MESSAGE_HEADER Header;
> > +    uint64_t Payload[HV_MESSAGE_MAX_PAYLOAD_QWORD_COUNT];
> > +} HV_MESSAGE;
> 
> ... this) isn't it rather
> 
> #define HV_MESSAGE_MAX_PAYLOAD_QWORD_COUNT \
>     ((HV_MESSAGE_SIZE - sizeof(HV_MESSAGE_HEADER) / 8)
> 

I need the definition for the array in the struct so that sizeof(HV_MESSAGE) == 
HV_MESSAGE_SIZE (for which there is a BUILD_BUG_ON()) later. It's also written 
that way in the spec. so I'd rather leave it as-is.

  Paul

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