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Use memory barriers defined by xen headers #28

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Use memory barriers defined by xen headers #28

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22 changes: 17 additions & 5 deletions varstored.c
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Original file line number Diff line number Diff line change
Expand Up @@ -73,10 +73,22 @@
#include "io_port.h"
#include "option.h"

/* Get the correct defines for memory barriers - do not fall
* back to those provided by the kernel */
/* from <xen-barrier.h> in 4.20.0 */

#define xen_barrier() asm volatile ( "" : : : "memory")
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@rosslagerwall rosslagerwall Oct 31, 2025 •
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Why is this added if it is not used?

Having said that, I think it might be preferable to simply include a copy of xen-barrier.h and #include it. It would be easier to keep up-to-date and mean less tat in this file.


#if defined(__i386__)
# define smp_mb() asm volatile ( "lock addl $0, -4(%%esp)" ::: "memory" )
#define xen_mb() asm volatile ( "lock addl $0, -4(%%esp)" ::: "memory" )
#elif defined(__x86_64__)
# define smp_mb() asm volatile ( "lock addl $0, -32(%%rsp)" ::: "memory" )
#define xen_mb() asm volatile ( "lock addl $0, -32(%%rsp)" ::: "memory" )
#elif defined(__arm__)
#define xen_mb() asm volatile ("dmb" : : : "memory")
#elif defined(__aarch64__)
#define xen_mb() asm volatile ("dmb sy" : : : "memory")
#else
#error "Define barriers"
#endif

#define IO_PORT_ADDRESS 0x0100
Expand Down Expand Up @@ -551,15 +563,15 @@ varstored_poll_iopage(unsigned int i)
fprintf(stderr, "IO request not ready\n");
return;
}
smp_mb();
xen_mb();

ioreq->state = STATE_IOREQ_INPROCESS;

handle_ioreq(ioreq);
smp_mb();
xen_mb();

ioreq->state = STATE_IORESP_READY;
smp_mb();
xen_mb();

xenevtchn_notify(varstored_state.evth, varstored_state.ioreq_local_port[i]);
}
Expand Down