Re: [PATCH RFC 1/4] xen PVonHVM: use E820_Reserved area for shared_info

[Konrad Rzeszutek Wilk]

On Tue, Jul 15, 2014 at 05:43:17PM +0200, Vitaly Kuznetsov wrote:
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> writes:
> 
> > On Tue, Jul 15, 2014 at 03:40:37PM +0200, Vitaly Kuznetsov wrote:
> >> From: Olaf Hering <olaf@xxxxxxxxx>
> >> 
> >> This is a respin of 00e37bdb0113a98408de42db85be002f21dbffd3
> >> ("xen PVonHVM: move shared_info to MMIO before kexec").
> >> 
> >> Currently kexec in a PVonHVM guest fails with a triple fault because the
> >> new kernel overwrites the shared info page. The exact failure depends on
> >> the size of the kernel image. This patch moves the pfn from RAM into an
> >> E820 reserved memory area.
> >> 
> >> The pfn containing the shared_info is located somewhere in RAM. This will
> >> cause trouble if the current kernel is doing a kexec boot into a new
> >> kernel. The new kernel (and its startup code) can not know where the pfn
> >> is, so it can not reserve the page. The hypervisor will continue to update
> >> the pfn, and as a result memory corruption occours in the new kernel.
> >> 
> >> The toolstack marks the memory area FC000000-FFFFFFFF as reserved in the
> >> E820 map. Within that range newer toolstacks (4.3+) will keep 1MB
> >> starting from FE700000 as reserved for guest use. Older Xen4 toolstacks
> >> will usually not allocate areas up to FE700000, so FE700000 is expected
> >> to work also with older toolstacks.
> >> 
> >> In Xen3 there is no reserved area at a fixed location. If the guest is
> >> started on such old hosts the shared_info page will be placed in RAM. As
> >> a result kexec can not be used.
> >
> > So this looks right, the one thing that we really need to check 
> > is e9daff24a266307943457086533041bd971d0ef9
> >
> >    This reverts commit 9d02b43dee0d7fb18dfb13a00915550b1a3daa9f.
> >
> >     We are doing this b/c on 32-bit PVonHVM with older hypervisors
> >     (Xen 4.1) it ends up bothing up the start_info. This is bad b/c
> >     we use it for the time keeping, and the timekeeping code loops
> >     forever - as the version field never changes. Olaf says to
> >     revert it, so lets do that.
> >
> > Could you kindly test that the migration on 32-bit PVHVM guests
> > on older hypervisors works?
> >
> 
> Sure, will do! Was there anything special about the setup or any 32-bit
> pvhvm guest migration (on 64-bit hypervisor I suppose) would fail? I can
> try checking both current and old versions to make sure the issue was
> acutually fixed.

Nothing fancy (well, it was SMP, so 4 CPUs). I did the 'save'/'restore' and the
guest would not restore properly.

Thank you!
> 
> >> 
> >> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> >> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >> (cherry picked from commit 9d02b43dee0d7fb18dfb13a00915550b1a3daa9f)
> >> 
> >> [On resume we need to reset the xen_vcpu_info, which the original
> >> patch did not do]
> >> 
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> >> ---
> >>  arch/x86/xen/enlighten.c | 74 ++++++++++++++++++++++++++++++++++++------------
> >>  arch/x86/xen/suspend.c   |  2 +-
> >>  arch/x86/xen/xen-ops.h   |  2 +-
> >>  3 files changed, 58 insertions(+), 20 deletions(-)
> >> 
> >> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> >> index ffb101e..a11af62 100644
> >> --- a/arch/x86/xen/enlighten.c
> >> +++ b/arch/x86/xen/enlighten.c
> >> @@ -1726,23 +1726,29 @@ asmlinkage __visible void __init xen_start_kernel(void)
> >>  #endif
> >>  }
> >>  
> >> -void __ref xen_hvm_init_shared_info(void)
> >> +#ifdef CONFIG_XEN_PVHVM
> >> +#define HVM_SHARED_INFO_ADDR 0xFE700000UL
> >> +static struct shared_info *xen_hvm_shared_info;
> >> +static unsigned long xen_hvm_sip_phys;
> >> +static int xen_major, xen_minor;
> >> +
> >> +static void xen_hvm_connect_shared_info(unsigned long pfn)
> >>  {
> >> -	int cpu;
> >>  	struct xen_add_to_physmap xatp;
> >> -	static struct shared_info *shared_info_page = 0;
> >>  
> >> -	if (!shared_info_page)
> >> -		shared_info_page = (struct shared_info *)
> >> -			extend_brk(PAGE_SIZE, PAGE_SIZE);
> >>  	xatp.domid = DOMID_SELF;
> >>  	xatp.idx = 0;
> >>  	xatp.space = XENMAPSPACE_shared_info;
> >> -	xatp.gpfn = __pa(shared_info_page) >> PAGE_SHIFT;
> >> +	xatp.gpfn = pfn;
> >>  	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
> >>  		BUG();
> >>  
> >> -	HYPERVISOR_shared_info = (struct shared_info *)shared_info_page;
> >> +}
> >> +static void __init xen_hvm_set_shared_info(struct shared_info *sip)
> >> +{
> >> +	int cpu;
> >> +
> >> +	HYPERVISOR_shared_info = sip;
> >>  
> >>  	/* xen_vcpu is a pointer to the vcpu_info struct in the shared_info
> >>  	 * page, we use it in the event channel upcall and in some pvclock
> >> @@ -1760,20 +1766,39 @@ void __ref xen_hvm_init_shared_info(void)
> >>  	}
> >>  }
> >>  
> >> -#ifdef CONFIG_XEN_PVHVM
> >> +/* Reconnect the shared_info pfn to a (new) mfn */
> >> +void xen_hvm_resume_shared_info(void)
> >> +{
> >> +	xen_hvm_connect_shared_info(xen_hvm_sip_phys >> PAGE_SHIFT);
> >> +	xen_hvm_set_shared_info(xen_hvm_shared_info);
> >> +}
> >> +
> >> +/* Xen tools prior to Xen 4 do not provide a E820_Reserved area for guest usage.
> >> + * On these old tools the shared info page will be placed in E820_Ram.
> >> + * Xen 4 provides a E820_Reserved area at 0xFC000000, and this code expects
> >> + * that nothing is mapped up to HVM_SHARED_INFO_ADDR.
> >> + * Xen 4.3+ provides an explicit 1MB area at HVM_SHARED_INFO_ADDR which is used
> >> + * here for the shared info page. */
> >> +static void __init xen_hvm_init_shared_info(void)
> >> +{
> >> +	if (xen_major < 4) {
> >> +		xen_hvm_shared_info = extend_brk(PAGE_SIZE, PAGE_SIZE);
> >> +		xen_hvm_sip_phys = __pa(xen_hvm_shared_info);
> >> +	} else {
> >> +		xen_hvm_sip_phys = HVM_SHARED_INFO_ADDR;
> >> +		set_fixmap(FIX_PARAVIRT_BOOTMAP, xen_hvm_sip_phys);
> >> +		xen_hvm_shared_info =
> >> +		(struct shared_info *)fix_to_virt(FIX_PARAVIRT_BOOTMAP);
> >> +	}
> >> +	xen_hvm_resume_shared_info();
> >> +}
> >> +
> >>  static void __init init_hvm_pv_info(void)
> >>  {
> >> -	int major, minor;
> >> -	uint32_t eax, ebx, ecx, edx, pages, msr, base;
> >> +	uint32_t  ecx, edx, pages, msr, base;
> >>  	u64 pfn;
> >>  
> >>  	base = xen_cpuid_base();
> >> -	cpuid(base + 1, &eax, &ebx, &ecx, &edx);
> >> -
> >> -	major = eax >> 16;
> >> -	minor = eax & 0xffff;
> >> -	printk(KERN_INFO "Xen version %d.%d.\n", major, minor);
> >> -
> >>  	cpuid(base + 2, &pages, &msr, &ecx, &edx);
> >>  
> >>  	pfn = __pa(hypercall_page);
> >> @@ -1828,10 +1853,23 @@ static void __init xen_hvm_guest_init(void)
> >>  
> >>  static uint32_t __init xen_hvm_platform(void)
> >>  {
> >> +	uint32_t eax, ebx, ecx, edx, base;
> >> +
> >>  	if (xen_pv_domain())
> >>  		return 0;
> >>  
> >> -	return xen_cpuid_base();
> >> +	base = xen_cpuid_base();
> >> +	if (!base)
> >> +		return 0;
> >> +
> >> +	cpuid(base + 1, &eax, &ebx, &ecx, &edx);
> >> +
> >> +	xen_major = eax >> 16;
> >> +	xen_minor = eax & 0xffff;
> >> +
> >> +	printk(KERN_INFO "Xen version %d.%d.\n", xen_major, xen_minor);
> >> +
> >> +	return 1;
> >>  }
> >>  
> >>  bool xen_hvm_need_lapic(void)
> >> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
> >> index c4df9db..8d6793e 100644
> >> --- a/arch/x86/xen/suspend.c
> >> +++ b/arch/x86/xen/suspend.c
> >> @@ -32,7 +32,7 @@ static void xen_hvm_post_suspend(int suspend_cancelled)
> >>  {
> >>  #ifdef CONFIG_XEN_PVHVM
> >>  	int cpu;
> >> -	xen_hvm_init_shared_info();
> >> +	xen_hvm_resume_shared_info();
> >>  	xen_callback_vector();
> >>  	xen_unplug_emulated_devices();
> >>  	if (xen_feature(XENFEAT_hvm_safe_pvclock)) {
> >> diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
> >> index 97d8765..d083e82 100644
> >> --- a/arch/x86/xen/xen-ops.h
> >> +++ b/arch/x86/xen/xen-ops.h
> >> @@ -43,7 +43,7 @@ void xen_enable_syscall(void);
> >>  void xen_vcpu_restore(void);
> >>  
> >>  void xen_callback_vector(void);
> >> -void xen_hvm_init_shared_info(void);
> >> +void xen_hvm_resume_shared_info(void);
> >>  void xen_unplug_emulated_devices(void);
> >>  
> >>  void __init xen_build_dynamic_phys_to_machine(void);
> >> -- 
> >> 1.9.3
> >> 
> 
> -- 
>   Vitaly
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