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x86/mm: {paging, sh}_{cmpxchg, write}_guest_entry() cannot fault

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As of 2d0557c5cb ("x86: Fold page_info lock into type_info") we
haven't been updating guest page table entries through linear page
tables anymore. All updates have been using domain mappings since then.
Drop the use of guest/user access helpers there, and hence also the
boolean return values of the involved functions.

update_intpte(), otoh, gets its boolean return type retained for now,
as we may want to bound the CMPXCHG retry loop, indicating failure to
the caller instead when the retry threshold got exceeded.

With this {,__}cmpxchg_user() become unused, so they too get dropped.
(In fact, dropping them was the motivation of making the change.)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
This commit is contained in:
Jan Beulich authored and Andrew Cooper committed 2020-10-06 12:28:37 +01:00
1 parent 35679b221e
commit 1bc30c076a
7 files changed
+27 -87
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xen/arch/x86/mm.c
+3 -3
View File
@@ -4033,7 +4033,7 @@ long do_mmu_update(
case PGT_writable_page:
perfc_incr(writable_mmu_updates);
if ( paging_write_guest_entry(v, va, req.val, mfn) )
paging_write_guest_entry(v, va, req.val, mfn);
rc = 0;
break;
}
@@ -4044,9 +4044,9 @@ long do_mmu_update(
else if ( get_page_type(page, PGT_writable_page) )
{
perfc_incr(writable_mmu_updates);
if ( paging_write_guest_entry(v, va, req.val, mfn) )
rc = 0;
paging_write_guest_entry(v, va, req.val, mfn);
put_page_type(page);
rc = 0;
}
put_page(page);
xen/arch/x86/mm/shadow/private.h
+2 -2
View File
@@ -396,9 +396,9 @@ int shadow_write_p2m_entry(struct p2m_domain *p2m, unsigned long gfn,
unsigned int level);
/* Functions that atomically write PV guest PT entries */
bool sh_write_guest_entry(struct vcpu *v, intpte_t *p, intpte_t new,
void sh_write_guest_entry(struct vcpu *v, intpte_t *p, intpte_t new,
mfn_t gmfn);
bool sh_cmpxchg_guest_entry(struct vcpu *v, intpte_t *p, intpte_t *old,
void sh_cmpxchg_guest_entry(struct vcpu *v, intpte_t *p, intpte_t *old,
intpte_t new, mfn_t gmfn);
/* Update all the things that are derived from the guest's CR0/CR3/CR4.
xen/arch/x86/mm/shadow/pv.c
+7 -15
View File
@@ -26,43 +26,35 @@
/*
* Write a new value into the guest pagetable, and update the shadows
* appropriately. Returns false if we page-faulted, true for success.
* appropriately.
*/
bool
void
sh_write_guest_entry(struct vcpu *v, intpte_t *p, intpte_t new, mfn_t gmfn)
{
unsigned int failed;
paging_lock(v->domain);
failed = __copy_to_user(p, &new, sizeof(new));
if ( failed != sizeof(new) )
write_atomic(p, new);
sh_validate_guest_entry(v, gmfn, p, sizeof(new));
paging_unlock(v->domain);
return !failed;
}
/*
* Cmpxchg a new value into the guest pagetable, and update the shadows
* appropriately. Returns false if we page-faulted, true if not.
* appropriately.
* N.B. caller should check the value of "old" to see if the cmpxchg itself
* was successful.
*/
bool
void
sh_cmpxchg_guest_entry(struct vcpu *v, intpte_t *p, intpte_t *old,
intpte_t new, mfn_t gmfn)
{
bool failed;
intpte_t t = *old;
intpte_t t;
paging_lock(v->domain);
failed = cmpxchg_user(p, t, new);
t = cmpxchg(p, *old, new);
if ( t == *old )
sh_validate_guest_entry(v, gmfn, p, sizeof(new));
*old = t;
paging_unlock(v->domain);
return !failed;
}
/*
xen/arch/x86/pv/mm.h
+2 -11
View File
@@ -43,9 +43,7 @@ static inline bool update_intpte(intpte_t *p, intpte_t old, intpte_t new,
#ifndef PTE_UPDATE_WITH_CMPXCHG
if ( !preserve_ad )
{
rv = paging_write_guest_entry(v, p, new, mfn);
}
paging_write_guest_entry(v, p, new, mfn);
else
#endif
{
@@ -58,14 +56,7 @@ static inline bool update_intpte(intpte_t *p, intpte_t old, intpte_t new,
if ( preserve_ad )
_new |= old & (_PAGE_ACCESSED | _PAGE_DIRTY);
rv = paging_cmpxchg_guest_entry(v, p, &t, _new, mfn);
if ( unlikely(rv == 0) )
{
gdprintk(XENLOG_WARNING,
"Failed to update %" PRIpte " -> %" PRIpte
": saw %" PRIpte "\n", old, _new, t);
break;
}
paging_cmpxchg_guest_entry(v, p, &t, _new, mfn);
if ( t == old )
break;
xen/arch/x86/pv/ro-page-fault.c
+3 -4
View File
@@ -168,10 +168,9 @@ static int ptwr_emulated_update(unsigned long addr, intpte_t *p_old,
if ( p_old )
{
ol1e = l1e_from_intpte(old);
if ( !paging_cmpxchg_guest_entry(v, &l1e_get_intpte(*pl1e),
&old, l1e_get_intpte(nl1e), mfn) )
ret = X86EMUL_UNHANDLEABLE;
else if ( l1e_get_intpte(ol1e) == old )
paging_cmpxchg_guest_entry(v, &l1e_get_intpte(*pl1e), &old,
l1e_get_intpte(nl1e), mfn);
if ( l1e_get_intpte(ol1e) == old )
ret = X86EMUL_OKAY;
else
{
xen/include/asm-x86/paging.h
+10 -9
View File
@@ -100,9 +100,9 @@ struct shadow_paging_mode {
#ifdef CONFIG_SHADOW_PAGING
void (*detach_old_tables )(struct vcpu *v);
#ifdef CONFIG_PV
bool (*write_guest_entry )(struct vcpu *v, intpte_t *p,
void (*write_guest_entry )(struct vcpu *v, intpte_t *p,
intpte_t new, mfn_t gmfn);
bool (*cmpxchg_guest_entry )(struct vcpu *v, intpte_t *p,
void (*cmpxchg_guest_entry )(struct vcpu *v, intpte_t *p,
intpte_t *old, intpte_t new,
mfn_t gmfn);
#endif
@@ -333,15 +333,15 @@ static inline void paging_update_paging_modes(struct vcpu *v)
* paging-assistance state appropriately. Returns false if we page-faulted,
* true for success.
*/
static inline bool paging_write_guest_entry(
static inline void paging_write_guest_entry(
struct vcpu *v, intpte_t *p, intpte_t new, mfn_t gmfn)
{
#ifdef CONFIG_SHADOW_PAGING
if ( unlikely(paging_mode_shadow(v->domain)) && paging_get_hostmode(v) )
return paging_get_hostmode(v)->shadow.write_guest_entry(v, p, new,
gmfn);
paging_get_hostmode(v)->shadow.write_guest_entry(v, p, new, gmfn);
else
#endif
return !__copy_to_user(p, &new, sizeof(new));
write_atomic(p, new);
}
@@ -351,15 +351,16 @@ static inline bool paging_write_guest_entry(
* true if not. N.B. caller should check the value of "old" to see if the
* cmpxchg itself was successful.
*/
static inline bool paging_cmpxchg_guest_entry(
static inline void paging_cmpxchg_guest_entry(
struct vcpu *v, intpte_t *p, intpte_t *old, intpte_t new, mfn_t gmfn)
{
#ifdef CONFIG_SHADOW_PAGING
if ( unlikely(paging_mode_shadow(v->domain)) && paging_get_hostmode(v) )
return paging_get_hostmode(v)->shadow.cmpxchg_guest_entry(v, p, old,
paging_get_hostmode(v)->shadow.cmpxchg_guest_entry(v, p, old,
new, gmfn);
else
#endif
return !cmpxchg_user(p, *old, new);
*old = cmpxchg(p, *old, new);
}
#endif /* CONFIG_PV */
xen/include/asm-x86/x86_64/system.h
-43
View File
@@ -59,47 +59,4 @@ static always_inline __uint128_t cmpxchg16b_local_(
__cmpxchg16b(_p, (void *)(o), (void *)(n)); \
})
/*
* This function causes value _o to be changed to _n at location _p.
* If this access causes a fault then we return 1, otherwise we return 0.
* If no fault occurs then _o is updated to the value we saw at _p. If this
* is the same as the initial value of _o then _n is written to location _p.
*/
#define __cmpxchg_user(_p, _o, _n, _oppre, _regtype) \
stac(); \
asm volatile ( \
"1: lock cmpxchg %"_oppre"[new], %[ptr]\n" \
"2:\n" \
".section .fixup,\"ax\"\n" \
"3: movl $1, %[rc]\n" \
" jmp 2b\n" \
".previous\n" \
_ASM_EXTABLE(1b, 3b) \
: "+a" (_o), [rc] "=r" (_rc), \
[ptr] "+m" (*(volatile typeof(*(_p)) *)(_p)) \
: [new] _regtype (_n), "[rc]" (0) \
: "memory"); \
clac()
#define cmpxchg_user(_p, _o, _n) \
({ \
int _rc; \
switch ( sizeof(*(_p)) ) \
{ \
case 1: \
__cmpxchg_user(_p, _o, _n, "b", "q"); \
break; \
case 2: \
__cmpxchg_user(_p, _o, _n, "w", "r"); \
break; \
case 4: \
__cmpxchg_user(_p, _o, _n, "k", "r"); \
break; \
case 8: \
__cmpxchg_user(_p, _o, _n, "q", "r"); \
break; \
} \
_rc; \
})
#endif /* __X86_64_SYSTEM_H__ */
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