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Message-ID: <20140715155045.GB7792@laptop.dumpdata.com>
Date: Tue, 15 Jul 2014 11:50:45 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: xen-devel@...ts.xenproject.org,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
David Vrabel <david.vrabel@...rix.com>,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Andrew Jones <drjones@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/4] xen PVonHVM: use E820_Reserved area for
shared_info
On Tue, Jul 15, 2014 at 05:43:17PM +0200, Vitaly Kuznetsov wrote:
> Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> writes:
>
> > On Tue, Jul 15, 2014 at 03:40:37PM +0200, Vitaly Kuznetsov wrote:
> >> From: Olaf Hering <olaf@...fle.de>
> >>
> >> 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@...fle.de>
> >> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> >> (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@...hat.com>
> >> ---
> >> 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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