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SubjectRe: [PATCH] x86/xen: support early interrupts in xen pv guests
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Sorry, Andy, forgot to Cc: you...

On 24/11/17 09:42, Juergen Gross wrote:
> Add early interrupt handlers activated by idt_setup_early_handler() to
> the handlers supported by Xen pv guests. This will allow for early
> WARN() calls not crashing the guest.
>
> Suggested-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> arch/x86/include/asm/segment.h | 12 ++++++++++++
> arch/x86/mm/extable.c | 4 +++-
> arch/x86/xen/enlighten_pv.c | 37 ++++++++++++++++++++++++-------------
> arch/x86/xen/xen-asm_64.S | 14 ++++++++++++++
> 4 files changed, 53 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
> index b20f9d623f9c..8f09012b92e7 100644
> --- a/arch/x86/include/asm/segment.h
> +++ b/arch/x86/include/asm/segment.h
> @@ -236,11 +236,23 @@
> */
> #define EARLY_IDT_HANDLER_SIZE 9
>
> +/*
> + * xen_early_idt_handler_array is for Xen pv guests: for each entry in
> + * early_idt_handler_array it contains a prequel in the form of
> + * pop %rcx; pop %r11; jmp early_idt_handler_array[i]; summing up to
> + * max 8 bytes.
> + */
> +#define XEN_EARLY_IDT_HANDLER_SIZE 8
> +
> #ifndef __ASSEMBLY__
>
> extern const char early_idt_handler_array[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_SIZE];
> extern void early_ignore_irq(void);
>
> +#if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
> +extern const char xen_early_idt_handler_array[NUM_EXCEPTION_VECTORS][XEN_EARLY_IDT_HANDLER_SIZE];
> +#endif
> +
> /*
> * Load a segment. Fall back on loading the zero segment if something goes
> * wrong. This variant assumes that loading zero fully clears the segment.
> diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
> index 3321b446b66c..88754bfd425f 100644
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -1,6 +1,7 @@
> #include <linux/extable.h>
> #include <linux/uaccess.h>
> #include <linux/sched/debug.h>
> +#include <xen/xen.h>
>
> #include <asm/fpu/internal.h>
> #include <asm/traps.h>
> @@ -212,8 +213,9 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
> * Old CPUs leave the high bits of CS on the stack
> * undefined. I'm not sure which CPUs do this, but at least
> * the 486 DX works this way.
> + * Xen pv domains are not using the default __KERNEL_CS.
> */
> - if (regs->cs != __KERNEL_CS)
> + if (!xen_pv_domain() && regs->cs != __KERNEL_CS)
> goto fail;
>
> /*
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 5b2b3f3f6531..f2414c6c5e7c 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -622,7 +622,7 @@ static struct trap_array_entry trap_array[] = {
> { simd_coprocessor_error, xen_simd_coprocessor_error, false },
> };
>
> -static bool get_trap_addr(void **addr, unsigned int ist)
> +static bool __ref get_trap_addr(void **addr, unsigned int ist)
> {
> unsigned int nr;
> bool ist_okay = false;
> @@ -644,6 +644,14 @@ static bool get_trap_addr(void **addr, unsigned int ist)
> }
> }
>
> + if (nr == ARRAY_SIZE(trap_array) &&
> + *addr >= (void *)early_idt_handler_array[0] &&
> + *addr < (void *)early_idt_handler_array[NUM_EXCEPTION_VECTORS]) {
> + nr = (*addr - (void *)early_idt_handler_array[0]) /
> + EARLY_IDT_HANDLER_SIZE;
> + *addr = (void *)xen_early_idt_handler_array[nr];
> + }
> +
> if (WARN_ON(ist != 0 && !ist_okay))
> return false;
>
> @@ -1262,6 +1270,21 @@ asmlinkage __visible void __init xen_start_kernel(void)
> xen_setup_gdt(0);
>
> xen_init_irq_ops();
> +
> + /* Let's presume PV guests always boot on vCPU with id 0. */
> + per_cpu(xen_vcpu_id, 0) = 0;
> +
> + /*
> + * Setup xen_vcpu early because idt_setup_early_handler needs it for
> + * local_irq_disable(), irqs_disabled().
> + *
> + * Don't do the full vcpu_info placement stuff until we have
> + * the cpu_possible_mask and a non-dummy shared_info.
> + */
> + xen_vcpu_info_reset(0);
> +
> + idt_setup_early_handler();
> +
> xen_init_capabilities();
>
> #ifdef CONFIG_X86_LOCAL_APIC
> @@ -1295,18 +1318,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
> */
> acpi_numa = -1;
> #endif
> - /* Let's presume PV guests always boot on vCPU with id 0. */
> - per_cpu(xen_vcpu_id, 0) = 0;
> -
> - /*
> - * Setup xen_vcpu early because start_kernel needs it for
> - * local_irq_disable(), irqs_disabled().
> - *
> - * Don't do the full vcpu_info placement stuff until we have
> - * the cpu_possible_mask and a non-dummy shared_info.
> - */
> - xen_vcpu_info_reset(0);
> -
> WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_pv, xen_cpu_dead_pv));
>
> local_irq_disable();
> diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
> index 8a10c9a9e2b5..417b339e5c8e 100644
> --- a/arch/x86/xen/xen-asm_64.S
> +++ b/arch/x86/xen/xen-asm_64.S
> @@ -15,6 +15,7 @@
>
> #include <xen/interface/xen.h>
>
> +#include <linux/init.h>
> #include <linux/linkage.h>
>
> .macro xen_pv_trap name
> @@ -54,6 +55,19 @@ xen_pv_trap entry_INT80_compat
> #endif
> xen_pv_trap hypervisor_callback
>
> + __INIT
> +ENTRY(xen_early_idt_handler_array)
> + i = 0
> + .rept NUM_EXCEPTION_VECTORS
> + pop %rcx
> + pop %r11
> + jmp early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE
> + i = i + 1
> + .fill xen_early_idt_handler_array + i*XEN_EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
> + .endr
> +END(xen_early_idt_handler_array)
> + __FINIT
> +
> hypercall_iret = hypercall_page + __HYPERVISOR_iret * 32
> /*
> * Xen64 iret frame:
>

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