[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC 1/4] xen PVonHVM: use E820_Reserved area for shared_info
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. >> >> 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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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