Date: Wed, 29 Mar 2023 07:52:31 GMT From: =?utf-8?Q?Roger=20Pau=20Monn=C3=A9?= <royger@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 9f3be3a6ec8e - main - xen: switch to using core atomics for synchronization Message-ID: <202303290752.32T7qVDv052068@gitrepo.freebsd.org>
next in thread | raw e-mail | index | archive | help
The branch main has been updated by royger: URL: https://cgit.FreeBSD.org/src/commit/?id=9f3be3a6ec8ec6096e3d6c715695a6560aabbb80 commit 9f3be3a6ec8ec6096e3d6c715695a6560aabbb80 Author: Elliott Mitchell <ehem+freebsd@m5p.com> AuthorDate: 2022-01-24 01:19:16 +0000 Commit: Roger Pau Monné <royger@FreeBSD.org> CommitDate: 2023-03-29 07:51:42 +0000 xen: switch to using core atomics for synchronization Now that the atomic macros are always genuinely atomic on x86, they can be used for synchronization with Xen. A single core VM isn't too unusual, but actual single core hardware is uncommon. Replace an open-coding of evtchn_clear_port() with the inline. Substantially inspired by work done by Julien Grall <julien@xen.org>, 2014-01-13 17:40:58. Reviewed by: royger MFC after: 1 week --- sys/amd64/include/xen/synch_bitops.h | 129 ------------------------------- sys/dev/xen/evtchn/evtchn_dev.c | 2 - sys/dev/xen/grant_table/grant_table.c | 34 ++++----- sys/i386/include/xen/synch_bitops.h | 138 ---------------------------------- sys/x86/xen/xen_intr.c | 4 +- sys/xen/evtchn/evtchnvar.h | 19 +++-- 6 files changed, 30 insertions(+), 296 deletions(-) diff --git a/sys/amd64/include/xen/synch_bitops.h b/sys/amd64/include/xen/synch_bitops.h deleted file mode 100644 index 746687aa91bd..000000000000 --- a/sys/amd64/include/xen/synch_bitops.h +++ /dev/null @@ -1,129 +0,0 @@ -#ifndef __XEN_SYNCH_BITOPS_H__ -#define __XEN_SYNCH_BITOPS_H__ - -/* - * Copyright 1992, Linus Torvalds. - * Heavily modified to provide guaranteed strong synchronisation - * when communicating with Xen or other guest OSes running on other CPUs. - */ - - -#define ADDR (*(volatile long *) addr) - -static __inline__ void synch_set_bit(int nr, volatile void * addr) -{ - __asm__ __volatile__ ( - "lock btsl %1,%0" - : "=m" (ADDR) : "Ir" (nr) : "memory" ); -} - -static __inline__ void synch_clear_bit(int nr, volatile void * addr) -{ - __asm__ __volatile__ ( - "lock btrl %1,%0" - : "=m" (ADDR) : "Ir" (nr) : "memory" ); -} - -static __inline__ void synch_change_bit(int nr, volatile void * addr) -{ - __asm__ __volatile__ ( - "lock btcl %1,%0" - : "=m" (ADDR) : "Ir" (nr) : "memory" ); -} - -static __inline__ int synch_test_and_set_bit(int nr, volatile void * addr) -{ - int oldbit; - __asm__ __volatile__ ( - "lock btsl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit), "=m" (ADDR) : "Ir" (nr) : "memory"); - return oldbit; -} - -static __inline__ int synch_test_and_clear_bit(int nr, volatile void * addr) -{ - int oldbit; - __asm__ __volatile__ ( - "lock btrl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit), "=m" (ADDR) : "Ir" (nr) : "memory"); - return oldbit; -} - -static __inline__ int synch_test_and_change_bit(int nr, volatile void * addr) -{ - int oldbit; - - __asm__ __volatile__ ( - "lock btcl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit), "=m" (ADDR) : "Ir" (nr) : "memory"); - return oldbit; -} - -struct __synch_xchg_dummy { unsigned long a[100]; }; -#define __synch_xg(x) ((volatile struct __synch_xchg_dummy *)(x)) - -#define synch_cmpxchg(ptr, old, new) \ -((__typeof__(*(ptr)))__synch_cmpxchg((ptr),\ - (unsigned long)(old), \ - (unsigned long)(new), \ - sizeof(*(ptr)))) - -static inline unsigned long __synch_cmpxchg(volatile void *ptr, - unsigned long old, - unsigned long new, int size) -{ - unsigned long prev; - switch (size) { - case 1: - __asm__ __volatile__("lock; cmpxchgb %b1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; - case 2: - __asm__ __volatile__("lock; cmpxchgw %w1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; - case 4: - __asm__ __volatile__("lock; cmpxchgl %k1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; - case 8: - __asm__ __volatile__("lock; cmpxchgq %1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; - } - return old; -} - -static __inline__ int synch_const_test_bit(int nr, const volatile void * addr) -{ - return ((1UL << (nr & 31)) & - (((const volatile unsigned int *) addr)[nr >> 5])) != 0; -} - -static __inline__ int synch_var_test_bit(int nr, volatile void * addr) -{ - int oldbit; - __asm__ __volatile__ ( - "btl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit) : "m" (ADDR), "Ir" (nr) ); - return oldbit; -} - -#define synch_test_bit(nr,addr) \ -(__builtin_constant_p(nr) ? \ - synch_const_test_bit((nr),(addr)) : \ - synch_var_test_bit((nr),(addr))) - -#endif /* __XEN_SYNCH_BITOPS_H__ */ diff --git a/sys/dev/xen/evtchn/evtchn_dev.c b/sys/dev/xen/evtchn/evtchn_dev.c index 34f481358008..a217120222e6 100644 --- a/sys/dev/xen/evtchn/evtchn_dev.c +++ b/sys/dev/xen/evtchn/evtchn_dev.c @@ -58,8 +58,6 @@ __FBSDID("$FreeBSD$"); #include <sys/filio.h> #include <sys/vnode.h> -#include <machine/xen/synch_bitops.h> - #include <xen/xen-os.h> #include <xen/evtchn.h> #include <xen/xen_intr.h> diff --git a/sys/dev/xen/grant_table/grant_table.c b/sys/dev/xen/grant_table/grant_table.c index fdbec8ac14e8..b5bbe04977a2 100644 --- a/sys/dev/xen/grant_table/grant_table.c +++ b/sys/dev/xen/grant_table/grant_table.c @@ -28,9 +28,6 @@ __FBSDID("$FreeBSD$"); #include <machine/cpu.h> #include <xen/xen-os.h> -#include <xen/hypervisor.h> -#include <machine/xen/synch_bitops.h> - #include <xen/hypervisor.h> #include <xen/gnttab.h> @@ -182,18 +179,15 @@ gnttab_query_foreign_access(grant_ref_t ref) int gnttab_end_foreign_access_ref(grant_ref_t ref) { - uint16_t flags, nflags; + uint16_t flags; - nflags = shared[ref].flags; - do { - if ( (flags = nflags) & (GTF_reading|GTF_writing) ) { - printf("%s: WARNING: g.e. still in use!\n", __func__); - return (0); - } - } while ((nflags = synch_cmpxchg(&shared[ref].flags, flags, 0)) != - flags); + while (!((flags = atomic_load_16(&shared[ref].flags)) & + (GTF_reading|GTF_writing))) + if (atomic_cmpset_16(&shared[ref].flags, flags, 0)) + return (1); - return (1); + printf("%s: WARNING: g.e. still in use!\n", __func__); + return (0); } void @@ -284,17 +278,21 @@ gnttab_end_foreign_transfer_ref(grant_ref_t ref) /* * If a transfer is not even yet started, try to reclaim the grant * reference and return failure (== 0). + * + * NOTE: This is a loop since the atomic cmpset can fail multiple + * times. In normal operation it will be rare to execute more than + * twice. Attempting an attack would consume a great deal of + * attacker resources and be unlikely to prolong the loop very much. */ - while (!((flags = shared[ref].flags) & GTF_transfer_committed)) { - if ( synch_cmpxchg(&shared[ref].flags, flags, 0) == flags ) + while (!((flags = atomic_load_16(&shared[ref].flags)) & + GTF_transfer_committed)) + if (atomic_cmpset_16(&shared[ref].flags, flags, 0)) return (0); - cpu_spinwait(); - } /* If a transfer is in progress then wait until it is completed. */ while (!(flags & GTF_transfer_completed)) { - flags = shared[ref].flags; cpu_spinwait(); + flags = atomic_load_16(&shared[ref].flags); } /* Read the frame number /after/ reading completion status. */ diff --git a/sys/i386/include/xen/synch_bitops.h b/sys/i386/include/xen/synch_bitops.h deleted file mode 100644 index 696bc6fa43f4..000000000000 --- a/sys/i386/include/xen/synch_bitops.h +++ /dev/null @@ -1,138 +0,0 @@ -#ifndef __XEN_SYNCH_BITOPS_H__ -#define __XEN_SYNCH_BITOPS_H__ - -/* - * Copyright 1992, Linus Torvalds. - * Heavily modified to provide guaranteed strong synchronisation - * when communicating with Xen or other guest OSes running on other CPUs. - */ - -#define ADDR (*(volatile long *) addr) - -static __inline__ void synch_set_bit(int nr, volatile void * addr) -{ - __asm__ __volatile__ ( - "lock btsl %1,%0" - : "=m" (ADDR) : "Ir" (nr) : "memory" ); -} - -static __inline__ void synch_clear_bit(int nr, volatile void * addr) -{ - __asm__ __volatile__ ( - "lock btrl %1,%0" - : "=m" (ADDR) : "Ir" (nr) : "memory" ); -} - -static __inline__ void synch_change_bit(int nr, volatile void * addr) -{ - __asm__ __volatile__ ( - "lock btcl %1,%0" - : "=m" (ADDR) : "Ir" (nr) : "memory" ); -} - -static __inline__ int synch_test_and_set_bit(int nr, volatile void * addr) -{ - int oldbit; - __asm__ __volatile__ ( - "lock btsl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit), "=m" (ADDR) : "Ir" (nr) : "memory"); - return oldbit; -} - -static __inline__ int synch_test_and_clear_bit(int nr, volatile void * addr) -{ - int oldbit; - __asm__ __volatile__ ( - "lock btrl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit), "=m" (ADDR) : "Ir" (nr) : "memory"); - return oldbit; -} - -static __inline__ int synch_test_and_change_bit(int nr, volatile void * addr) -{ - int oldbit; - - __asm__ __volatile__ ( - "lock btcl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit), "=m" (ADDR) : "Ir" (nr) : "memory"); - return oldbit; -} - -struct __synch_xchg_dummy { unsigned long a[100]; }; -#define __synch_xg(x) ((volatile struct __synch_xchg_dummy *)(x)) - -#define synch_cmpxchg(ptr, old, new) \ -((__typeof__(*(ptr)))__synch_cmpxchg((ptr),\ - (unsigned long)(old), \ - (unsigned long)(new), \ - sizeof(*(ptr)))) - -static inline unsigned long __synch_cmpxchg(volatile void *ptr, - unsigned long old, - unsigned long new, int size) -{ - unsigned long prev; - switch (size) { - case 1: - __asm__ __volatile__("lock; cmpxchgb %b1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; - case 2: - __asm__ __volatile__("lock; cmpxchgw %w1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; -#ifdef CONFIG_X86_64 - case 4: - __asm__ __volatile__("lock; cmpxchgl %k1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; - case 8: - __asm__ __volatile__("lock; cmpxchgq %1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; -#else - case 4: - __asm__ __volatile__("lock; cmpxchgl %1,%2" - : "=a"(prev) - : "q"(new), "m"(*__synch_xg(ptr)), - "0"(old) - : "memory"); - return prev; -#endif - } - return old; -} - -static __inline__ int synch_const_test_bit(int nr, const volatile void * addr) -{ - return ((1UL << (nr & 31)) & - (((const volatile unsigned int *) addr)[nr >> 5])) != 0; -} - -static __inline__ int synch_var_test_bit(int nr, volatile void * addr) -{ - int oldbit; - __asm__ __volatile__ ( - "btl %2,%1\n\tsbbl %0,%0" - : "=r" (oldbit) : "m" (ADDR), "Ir" (nr) ); - return oldbit; -} - -#define synch_test_bit(nr,addr) \ -(__builtin_constant_p(nr) ? \ - synch_const_test_bit((nr),(addr)) : \ - synch_var_test_bit((nr),(addr))) - -#endif /* __XEN_SYNCH_BITOPS_H__ */ diff --git a/sys/x86/xen/xen_intr.c b/sys/x86/xen/xen_intr.c index cf4560b6b5fb..8d5562e21018 100644 --- a/sys/x86/xen/xen_intr.c +++ b/sys/x86/xen/xen_intr.c @@ -57,8 +57,6 @@ __FBSDID("$FreeBSD$"); #include <machine/smp.h> #include <machine/stdarg.h> -#include <machine/xen/synch_bitops.h> - #include <xen/xen-os.h> #include <xen/hvm.h> #include <xen/hypervisor.h> @@ -576,7 +574,7 @@ xen_intr_handle_upcall(struct trapframe *trap_frame) /* process port */ port = (l1i * LONG_BIT) + l2i; - synch_clear_bit(port, &s->evtchn_pending[0]); + evtchn_clear_port(port); isrc = xen_intr_port_to_isrc[port]; if (__predict_false(isrc == NULL)) diff --git a/sys/xen/evtchn/evtchnvar.h b/sys/xen/evtchn/evtchnvar.h index 1f78755115ac..d1438846594f 100644 --- a/sys/xen/evtchn/evtchnvar.h +++ b/sys/xen/evtchn/evtchnvar.h @@ -6,6 +6,7 @@ * * Copyright (c) 2004, K A Fraser * Copyright (c) 2012, Spectra Logic Corporation + * Copyright © 2022, Elliott Mitchell * * This file may be distributed separately from the Linux kernel, or * incorporated into other software packages, subject to the following license: @@ -48,6 +49,12 @@ enum evtchn_type { /** Submit a port notification for delivery to a userland evtchn consumer */ void evtchn_device_upcall(evtchn_port_t port); +/* Macros for accessing event channel values */ +#define EVTCHN_PTR(type, port) \ + (HYPERVISOR_shared_info->evtchn_##type + ((port) / __LONG_BIT)) +#define EVTCHN_BIT(port) ((port) & (__LONG_BIT - 1)) +#define EVTCHN_MASK(port) (1UL << EVTCHN_BIT(port)) + /** * Disable signal delivery for an event channel port, returning its * previous mask state. @@ -59,8 +66,9 @@ void evtchn_device_upcall(evtchn_port_t port); static inline int evtchn_test_and_set_mask(evtchn_port_t port) { - shared_info_t *s = HYPERVISOR_shared_info; - return synch_test_and_set_bit(port, s->evtchn_mask); + + return (atomic_testandset_long(EVTCHN_PTR(mask, port), + EVTCHN_BIT(port))); } /** @@ -71,8 +79,8 @@ evtchn_test_and_set_mask(evtchn_port_t port) static inline void evtchn_clear_port(evtchn_port_t port) { - shared_info_t *s = HYPERVISOR_shared_info; - synch_clear_bit(port, &s->evtchn_pending[0]); + + atomic_clear_long(EVTCHN_PTR(pending, port), EVTCHN_MASK(port)); } /** @@ -83,9 +91,8 @@ evtchn_clear_port(evtchn_port_t port) static inline void evtchn_mask_port(evtchn_port_t port) { - shared_info_t *s = HYPERVISOR_shared_info; - synch_set_bit(port, &s->evtchn_mask[0]); + atomic_set_long(EVTCHN_PTR(mask, port), EVTCHN_MASK(port)); } /**
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202303290752.32T7qVDv052068>