Date: Fri, 16 Dec 2011 13:00:14 -0800 From: Sean Bruno <seanbru@yahoo-inc.com> To: Alan Cox <alc@rice.edu> Cc: Alan Cox <alc@cs.rice.edu>, "xen@freebsd.org" <xen@freebsd.org> Subject: Re: PV i386 patch Message-ID: <1324069214.2669.6.camel@hitfishpass-lx.corp.yahoo.com> In-Reply-To: <4EEB9CCE.6090701@rice.edu> References: <4EEB9CCE.6090701@rice.edu>
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I'll test this out on the VMs in the fbsd cluster later.
Sean
On Fri, 2011-12-16 at 11:32 -0800, Alan Cox wrote:
> Is anyone here actively working on fixing problems with SMP support
> under PV i386? While doing some other maintenance on the
> vm_page_alloc() callers in the source tree, I happened to take a look at
> cpu_initialize_context() in mp_machdep.c. This function is involved in
> bringing up the 2nd, 3rd, etc. CPUs on an SMP system. I spotted a
> couple obvious errors. First, the size parameter given to kmem_*()
> functions is expected to be in terms of bytes and not pages. Second, I
> believe that PV i386 requires PAE to be used. If so, there are out of
> range accesses to the array m[].
>
> Index: i386/xen/mp_machdep.c
> ===================================================================
> --- i386/xen/mp_machdep.c (revision 228561)
> +++ i386/xen/mp_machdep.c (working copy)
> @@ -810,7 +810,7 @@ cpu_initialize_context(unsigned int cpu)
> {
> /* vcpu_guest_context_t is too large to allocate on the stack.
> * Hence we allocate statically and protect it with a lock */
> - vm_page_t m[4];
> + vm_page_t m[NPGPTD + 2];
> static vcpu_guest_context_t ctxt;
> vm_offset_t boot_stack;
> vm_offset_t newPTD;
> @@ -831,8 +831,8 @@ cpu_initialize_context(unsigned int cpu)
> pmap_zero_page(m[i]);
>
> }
> - boot_stack = kmem_alloc_nofault(kernel_map, 1);
> - newPTD = kmem_alloc_nofault(kernel_map, NPGPTD);
> + boot_stack = kmem_alloc_nofault(kernel_map, PAGE_SIZE);
> + newPTD = kmem_alloc_nofault(kernel_map, NPGPTD * PAGE_SIZE);
> ma[0] = VM_PAGE_TO_MACH(m[0])|PG_V;
>
> #ifdef PAE
> @@ -854,7 +854,7 @@ cpu_initialize_context(unsigned int cpu)
> nkpt*sizeof(vm_paddr_t));
>
> pmap_qremove(newPTD, 4);
> - kmem_free(kernel_map, newPTD, 4);
> + kmem_free(kernel_map, newPTD, 4 * PAGE_SIZE);
> /*
> * map actual idle stack to boot_stack
> */
>
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