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Message-ID: <87vbqytyp6.fsf@vitty.brq.redhat.com>
Date: Tue, 15 Jul 2014 17:43:17 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.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
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.
>>
>> 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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