[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen stable-4.16] x86/altp2m: help gcc13 to avoid it emitting a warning
commit cdde3171a2a932a6836b094c4387412e27414ec9 Author: Jan Beulich <jbeulich@xxxxxxxx> AuthorDate: Tue Mar 21 13:51:42 2023 +0100 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Tue Mar 21 13:51:42 2023 +0100 x86/altp2m: help gcc13 to avoid it emitting a warning Switches of altp2m-s always expect a valid altp2m to be in place (and indeed altp2m_vcpu_initialise() sets the active one to be at index 0). The compiler, however, cannot know that, and hence it cannot eliminate p2m_get_altp2m()'s case of returnin (literal) NULL. If then the compiler decides to special case that code path in the caller, the dereference in instances of atomic_dec(&p2m_get_altp2m(v)->active_vcpus); can, to the code generator, appear to be NULL dereferences, leading to In function 'atomic_dec', inlined from '...' at ...: ./arch/x86/include/asm/atomic.h:182:5: error: array subscript 0 is outside array bounds of 'int[0]' [-Werror=array-bounds=] Aid the compiler by adding a BUG_ON() checking the return value of the problematic p2m_get_altp2m(). Since with the use of the local variable the 2nd p2m_get_altp2m() each will look questionable at the first glance (Why is the local variable not used here?), open-code the only relevant piece of p2m_get_altp2m() there. To avoid repeatedly doing these transformations, and also to limit how "bad" the open-coding really is, convert the entire operation to an inline helper, used by all three instances (and accepting the redundant BUG_ON(idx >= MAX_ALTP2M) in two of the three cases). Reported-by: Charles Arnold <carnold@xxxxxxxx> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> master commit: be62b1fc2aa7375d553603fca07299da765a89fe master date: 2023-03-13 15:16:21 +0100 --- xen/arch/x86/hvm/vmx/vmx.c | 8 +------- xen/arch/x86/mm/p2m.c | 14 ++------------ xen/include/asm-x86/p2m.h | 20 ++++++++++++++++++++ 3 files changed, 23 insertions(+), 19 deletions(-) diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index 094141be9a..c8a839cd5e 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -4036,13 +4036,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) } } - if ( idx != vcpu_altp2m(v).p2midx ) - { - BUG_ON(idx >= MAX_ALTP2M); - atomic_dec(&p2m_get_altp2m(v)->active_vcpus); - vcpu_altp2m(v).p2midx = idx; - atomic_inc(&p2m_get_altp2m(v)->active_vcpus); - } + p2m_set_altp2m(v, idx); } /* XXX: This looks ugly, but we need a mechanism to ensure diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c index 8781df9dda..2d41446a69 100644 --- a/xen/arch/x86/mm/p2m.c +++ b/xen/arch/x86/mm/p2m.c @@ -2194,13 +2194,8 @@ bool_t p2m_switch_vcpu_altp2m_by_id(struct vcpu *v, unsigned int idx) if ( d->arch.altp2m_eptp[idx] != mfn_x(INVALID_MFN) ) { - if ( idx != vcpu_altp2m(v).p2midx ) - { - atomic_dec(&p2m_get_altp2m(v)->active_vcpus); - vcpu_altp2m(v).p2midx = idx; - atomic_inc(&p2m_get_altp2m(v)->active_vcpus); + if ( p2m_set_altp2m(v, idx) ) altp2m_vcpu_update_p2m(v); - } rc = 1; } @@ -2471,13 +2466,8 @@ int p2m_switch_domain_altp2m_by_id(struct domain *d, unsigned int idx) if ( d->arch.altp2m_visible_eptp[idx] != mfn_x(INVALID_MFN) ) { for_each_vcpu( d, v ) - if ( idx != vcpu_altp2m(v).p2midx ) - { - atomic_dec(&p2m_get_altp2m(v)->active_vcpus); - vcpu_altp2m(v).p2midx = idx; - atomic_inc(&p2m_get_altp2m(v)->active_vcpus); + if ( p2m_set_altp2m(v, idx) ) altp2m_vcpu_update_p2m(v); - } rc = 0; } diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h index 2db9ab0122..f92bb97394 100644 --- a/xen/include/asm-x86/p2m.h +++ b/xen/include/asm-x86/p2m.h @@ -841,6 +841,26 @@ static inline struct p2m_domain *p2m_get_altp2m(struct vcpu *v) return v->domain->arch.altp2m_p2m[index]; } +/* set current alternate p2m table */ +static inline bool p2m_set_altp2m(struct vcpu *v, unsigned int idx) +{ + struct p2m_domain *orig; + + BUG_ON(idx >= MAX_ALTP2M); + + if ( idx == vcpu_altp2m(v).p2midx ) + return false; + + orig = p2m_get_altp2m(v); + BUG_ON(!orig); + atomic_dec(&orig->active_vcpus); + + vcpu_altp2m(v).p2midx = idx; + atomic_inc(&v->domain->arch.altp2m_p2m[idx]->active_vcpus); + + return true; +} + /* Switch alternate p2m for a single vcpu */ bool_t p2m_switch_vcpu_altp2m_by_id(struct vcpu *v, unsigned int idx); -- generated by git-patchbot for /home/xen/git/xen.git#stable-4.16
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