Re: [PATCH 1/2] xen/arm: Convert runstate address during hypcall

[Bertrand Marquis <Bertrand.Marquis@arm.com>]

> On 11 Jun 2020, at 19:16, Stefano Stabellini <sstabellini@kernel.org> wrote:
> 
> On Thu, 11 Jun 2020, Bertrand Marquis wrote:
>> At the moment on Arm, a Linux guest running with KTPI enabled will
>> cause the following error when a context switch happens in user mode:
>> (XEN) p2m.c:1890: d1v0: Failed to walk page-table va 0xffffff837ebe0cd0
>> 
>> This patch is modifying the register runstate area handling on arm to
>> convert the guest address during the hypercall. During runtime context
>> switches the area is mapped to update the guest runstate copy.
>> The patch is also removing the initial copy which was done during the
>> hypercall handling as this is done on the current core when the context
>> is restore to go back to guest execution on arm.
>> 
>> As a consequence if the register runstate hypercall is called on one
>> vcpu for an other vcpu, the area will not be updated until the vcpu
>> will be executed (on arm only).
>> 
>> On x86, the behaviour is not modified, the address conversion is done
>> during the context switch and the area is updated fully during the
>> hypercall.
>> inline functions in headers could not be used as the architecture
>> domain.h is included before the global domain.h making it impossible
>> to use the struct vcpu inside the architecture header.
>> This should not have any performance impact as the hypercall is only
>> called once per vcpu usually.
>> 
>> Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
>> ---
>> xen/arch/arm/domain.c        | 109 +++++++++++++++++++++++++++++------
>> xen/arch/x86/domain.c        |  30 +++++++++-
>> xen/arch/x86/x86_64/domain.c |   4 +-
>> xen/common/domain.c          |  19 ++----
>> xen/include/asm-arm/domain.h |   8 +++
>> xen/include/asm-x86/domain.h |  16 +++++
>> xen/include/xen/domain.h     |   4 ++
>> xen/include/xen/sched.h      |  16 +----
>> 8 files changed, 153 insertions(+), 53 deletions(-)
>> 
>> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
>> index 31169326b2..739059234f 100644
>> --- a/xen/arch/arm/domain.c
>> +++ b/xen/arch/arm/domain.c
>> @@ -19,6 +19,7 @@
>> #include <xen/sched.h>
>> #include <xen/softirq.h>
>> #include <xen/wait.h>
>> +#include <xen/domain_page.h>
>> 
>> #include <asm/alternative.h>
>> #include <asm/cpuerrata.h>
>> @@ -275,36 +276,104 @@ static void ctxt_switch_to(struct vcpu *n)
>>     virt_timer_restore(n);
>> }
>> 
>> -/* Update per-VCPU guest runstate shared memory area (if registered). */
>> -static void update_runstate_area(struct vcpu *v)
>> +void arch_cleanup_runstate_guest(struct vcpu *v)
>> {
>> -    void __user *guest_handle = NULL;
>> -    struct vcpu_runstate_info runstate;
>> +    spin_lock(&v->arch.runstate_guest.lock);
>> 
>> -    if ( guest_handle_is_null(runstate_guest(v)) )
>> -        return;
>> +    /* cleanup previous page if any */
>> +    if ( v->arch.runstate_guest.page )
>> +    {
>> +        put_page_and_type(v->arch.runstate_guest.page);
>> +        v->arch.runstate_guest.page = NULL;
>> +        v->arch.runstate_guest.offset = 0;
>> +    }
>> 
>> -    memcpy(&runstate, &v->runstate, sizeof(runstate));
>> +    spin_unlock(&v->arch.runstate_guest.lock);
>> +}
>> 
>> -    if ( VM_ASSIST(v->domain, runstate_update_flag) )
>> +int arch_setup_runstate_guest(struct vcpu *v,
>> +                            struct vcpu_register_runstate_memory_area area)
>> +{
>> +    struct page_info *page;
>> +    unsigned offset;
>> +
>> +    spin_lock(&v->arch.runstate_guest.lock);
>> +
>> +    /* cleanup previous page if any */
>> +    if ( v->arch.runstate_guest.page )
>>     {
>> -        guest_handle = &v->runstate_guest.p->state_entry_time + 1;
>> -        guest_handle--;
>> -        runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
>> -        __raw_copy_to_guest(guest_handle,
>> -                            (void *)(&runstate.state_entry_time + 1) - 1, 1);
>> -        smp_wmb();
>> +        put_page_and_type(v->arch.runstate_guest.page);
>> +        v->arch.runstate_guest.page = NULL;
>> +        v->arch.runstate_guest.offset = 0;
>> +    }
>> +
>> +    offset = ((vaddr_t)area.addr.v) & ~PAGE_MASK;
>> +    if ( offset > (PAGE_SIZE - sizeof(struct vcpu_runstate_info)) )
>> +    {
>> +        spin_unlock(&v->arch.runstate_guest.lock);
>> +        gprintk(XENLOG_DEBUG, "Runstate is crossing pages\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    /* provided address must be aligned to a 64bit */
>> +    if ( offset % alignof(struct vcpu_runstate_info) )
>> +    {
>> +        spin_unlock(&v->arch.runstate_guest.lock);
>> +        gprintk(XENLOG_DEBUG, "Runstate pointer is not aligned\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    page = get_page_from_gva(v, (vaddr_t)area.addr.v, GV2M_WRITE);
>> +    if ( !page )
>> +    {
>> +        spin_unlock(&v->arch.runstate_guest.lock);
>> +        gprintk(XENLOG_DEBUG, "Runstate pointer is not mapped\n");
> 
> I would make all these XENLOG_WARNING or XENLOG_ERR, they are errors
> after all. This last one I'd say "Could not map runstate point" and also
> print the address.

Ok I will fix it to Warning and change the message like this.

> 
> 
>> +        return -EINVAL;
>>     }
>> 
>> -    __copy_to_guest(runstate_guest(v), &runstate, 1);
>> +    v->arch.runstate_guest.page = page;
>> +    v->arch.runstate_guest.offset = offset;
>> +
>> +    spin_unlock(&v->arch.runstate_guest.lock);
>> +
>> +    return 0;
>> +}
>> +
>> +
>> +/* Update per-VCPU guest runstate shared memory area (if registered). */
>> +static void update_runstate_area(struct vcpu *v)
>> +{
>> +    struct vcpu_runstate_info *guest_runstate;
>> +    void *p;
>> +
>> +    spin_lock(&v->arch.runstate_guest.lock);
>> 
>> -    if ( guest_handle )
>> +    if ( v->arch.runstate_guest.page )
>>     {
>> -        runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
>> +        p = __map_domain_page(v->arch.runstate_guest.page);
>> +        guest_runstate = p + v->arch.runstate_guest.offset;
>> +
>> +        if ( VM_ASSIST(v->domain, runstate_update_flag) )
>> +        {
>> +            v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
>> +            guest_runstate->state_entry_time |= XEN_RUNSTATE_UPDATE;
> 
> I think that this write to guest_runstate should use write_atomic or
> another atomic write operation.

I will answer at the end of the discussion on the subject.

> 
> 
>> +            smp_wmb();
>> +        }
>> +
>> +        memcpy(guest_runstate, &v->runstate, sizeof(v->runstate));
>>         smp_wmb();
>> -        __raw_copy_to_guest(guest_handle,
>> -                            (void *)(&runstate.state_entry_time + 1) - 1, 1);
>> +
>> +        if ( VM_ASSIST(v->domain, runstate_update_flag) )
>> +        {
>> +            v->runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
>> +            guest_runstate->state_entry_time &= ~XEN_RUNSTATE_UPDATE;
> 
> same here
> 
> 
>> +            smp_wmb();
>> +        }
>> +
>> +        unmap_domain_page(p);
>>     }
>> +
>> +    spin_unlock(&v->arch.runstate_guest.lock);
>> }
>> 
>> static void schedule_tail(struct vcpu *prev)
>> @@ -560,6 +629,8 @@ int arch_vcpu_create(struct vcpu *v)
>>     v->arch.saved_context.sp = (register_t)v->arch.cpu_info;
>>     v->arch.saved_context.pc = (register_t)continue_new_vcpu;
>> 
>> +    spin_lock_init(&v->arch.runstate_guest.lock);
>> +
>>     /* Idle VCPUs don't need the rest of this setup */
>>     if ( is_idle_vcpu(v) )
>>         return rc;
>> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
>> index fee6c3931a..32bbed87d5 100644
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -1642,6 +1642,30 @@ void paravirt_ctxt_switch_to(struct vcpu *v)
>>         wrmsr_tsc_aux(v->arch.msrs->tsc_aux);
>> }
>> 
>> +int arch_setup_runstate_guest(struct vcpu *v,
>> +                             struct vcpu_register_runstate_memory_area area)
>> +{
>> +    struct vcpu_runstate_info runstate;
>> +
>> +    runstate_guest(v) = area.addr.h;
>> +
>> +    if ( v == current )
>> +    {
>> +        __copy_to_guest(runstate_guest(v), &v->runstate, 1);
>> +    }
>> +    else
>> +    {
>> +        vcpu_runstate_get(v, &runstate);
>> +        __copy_to_guest(runstate_guest(v), &runstate, 1);
>> +    }
>> +    return 0;
>> +}
>> +
>> +void arch_cleanup_runstate_guest(struct vcpu *v)
>> +{
>> +    set_xen_guest_handle(runstate_guest(v), NULL);
>> +}
>> +
>> /* Update per-VCPU guest runstate shared memory area (if registered). */
>> bool update_runstate_area(struct vcpu *v)
>> {
>> @@ -1660,8 +1684,8 @@ bool update_runstate_area(struct vcpu *v)
>>     if ( VM_ASSIST(v->domain, runstate_update_flag) )
>>     {
>>         guest_handle = has_32bit_shinfo(v->domain)
>> -            ? &v->runstate_guest.compat.p->state_entry_time + 1
>> -            : &v->runstate_guest.native.p->state_entry_time + 1;
>> +            ? &v->arch.runstate_guest.compat.p->state_entry_time + 1
>> +            : &v->arch.runstate_guest.native.p->state_entry_time + 1;
>>         guest_handle--;
>>         runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
>>         __raw_copy_to_guest(guest_handle,
>> @@ -1674,7 +1698,7 @@ bool update_runstate_area(struct vcpu *v)
>>         struct compat_vcpu_runstate_info info;
>> 
>>         XLAT_vcpu_runstate_info(&info, &runstate);
>> -        __copy_to_guest(v->runstate_guest.compat, &info, 1);
>> +        __copy_to_guest(v->arch.runstate_guest.compat, &info, 1);
>>         rc = true;
>>     }
>>     else
>> diff --git a/xen/arch/x86/x86_64/domain.c b/xen/arch/x86/x86_64/domain.c
>> index c46dccc25a..b879e8dd2c 100644
>> --- a/xen/arch/x86/x86_64/domain.c
>> +++ b/xen/arch/x86/x86_64/domain.c
>> @@ -36,7 +36,7 @@ arch_compat_vcpu_op(
>>             break;
>> 
>>         rc = 0;
>> -        guest_from_compat_handle(v->runstate_guest.compat, area.addr.h);
>> +        guest_from_compat_handle(v->arch.runstate_guest.compat, area.addr.h);
>> 
>>         if ( v == current )
>>         {
>> @@ -49,7 +49,7 @@ arch_compat_vcpu_op(
>>             vcpu_runstate_get(v, &runstate);
>>             XLAT_vcpu_runstate_info(&info, &runstate);
>>         }
>> -        __copy_to_guest(v->runstate_guest.compat, &info, 1);
>> +        __copy_to_guest(v->arch.runstate_guest.compat, &info, 1);
>> 
>>         break;
>>     }
>> diff --git a/xen/common/domain.c b/xen/common/domain.c
>> index 7cc9526139..0ca6bf4dbc 100644
>> --- a/xen/common/domain.c
>> +++ b/xen/common/domain.c
>> @@ -727,7 +727,10 @@ int domain_kill(struct domain *d)
>>         if ( cpupool_move_domain(d, cpupool0) )
>>             return -ERESTART;
>>         for_each_vcpu ( d, v )
>> +        {
>> +            arch_cleanup_runstate_guest(v);
>>             unmap_vcpu_info(v);
>> +        }
>>         d->is_dying = DOMDYING_dead;
>>         /* Mem event cleanup has to go here because the rings 
>>          * have to be put before we call put_domain. */
>> @@ -1167,7 +1170,7 @@ int domain_soft_reset(struct domain *d)
>> 
>>     for_each_vcpu ( d, v )
>>     {
>> -        set_xen_guest_handle(runstate_guest(v), NULL);
>> +        arch_cleanup_runstate_guest(v);
>>         unmap_vcpu_info(v);
>>     }
>> 
>> @@ -1484,7 +1487,6 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
>>     case VCPUOP_register_runstate_memory_area:
>>     {
>>         struct vcpu_register_runstate_memory_area area;
>> -        struct vcpu_runstate_info runstate;
>> 
>>         rc = -EFAULT;
>>         if ( copy_from_guest(&area, arg, 1) )
>> @@ -1493,18 +1495,7 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
>>         if ( !guest_handle_okay(area.addr.h, 1) )
>>             break;
>> 
>> -        rc = 0;
>> -        runstate_guest(v) = area.addr.h;
>> -
>> -        if ( v == current )
>> -        {
>> -            __copy_to_guest(runstate_guest(v), &v->runstate, 1);
>> -        }
>> -        else
>> -        {
>> -            vcpu_runstate_get(v, &runstate);
>> -            __copy_to_guest(runstate_guest(v), &runstate, 1);
>> -        }
>> +        rc = arch_setup_runstate_guest(v, area);
>> 
>>         break;
>>     }
>> diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
>> index 4e2f582006..3a7f53e13d 100644
>> --- a/xen/include/asm-arm/domain.h
>> +++ b/xen/include/asm-arm/domain.h
>> @@ -11,6 +11,7 @@
>> #include <asm/vgic.h>
>> #include <asm/vpl011.h>
>> #include <public/hvm/params.h>
>> +#include <public/vcpu.h>
>> #include <xen/serial.h>
>> #include <xen/rbtree.h>
>> 
>> @@ -206,6 +207,13 @@ struct arch_vcpu
>>      */
>>     bool need_flush_to_ram;
>> 
>> +    /* runstate guest info */
>> +    struct {
>> +        struct page_info *page;  /* guest page */
>> +        unsigned         offset; /* offset in page */
>> +        spinlock_t       lock;   /* lock to access page */
>> +    } runstate_guest;
>> +
>> }  __cacheline_aligned;
>> 
>> void vcpu_show_execution_state(struct vcpu *);
>> diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
>> index e8cee3d5e5..f917b48cb8 100644
>> --- a/xen/include/asm-x86/domain.h
>> +++ b/xen/include/asm-x86/domain.h
>> @@ -11,6 +11,11 @@
>> #include <asm/x86_emulate.h>
>> #include <public/vcpu.h>
>> #include <public/hvm/hvm_info_table.h>
>> +#ifdef CONFIG_COMPAT
>> +#include <compat/vcpu.h>
>> +DEFINE_XEN_GUEST_HANDLE(vcpu_runstate_info_compat_t);
>> +#endif
>> +
>> 
>> #define has_32bit_shinfo(d)    ((d)->arch.has_32bit_shinfo)
>> 
>> @@ -626,6 +631,17 @@ struct arch_vcpu
>>     struct {
>>         bool next_interrupt_enabled;
>>     } monitor;
>> +
>> +#ifndef CONFIG_COMPAT
>> +# define runstate_guest(v) ((v)->arch.runstate_guest)
>> +    XEN_GUEST_HANDLE(vcpu_runstate_info_t) runstate_guest; /* guest address */
>> +#else
>> +# define runstate_guest(v) ((v)->arch.runstate_guest.native)
>> +    union {
>> +        XEN_GUEST_HANDLE(vcpu_runstate_info_t) native;
>> +        XEN_GUEST_HANDLE(vcpu_runstate_info_compat_t) compat;
>> +    } runstate_guest;
>> +#endif
>> };
>> 
>> struct guest_memory_policy
>> diff --git a/xen/include/xen/domain.h b/xen/include/xen/domain.h
>> index 7e51d361de..d5d73ce997 100644
>> --- a/xen/include/xen/domain.h
>> +++ b/xen/include/xen/domain.h
>> @@ -63,6 +63,10 @@ void arch_vcpu_destroy(struct vcpu *v);
>> int map_vcpu_info(struct vcpu *v, unsigned long gfn, unsigned offset);
>> void unmap_vcpu_info(struct vcpu *v);
>> 
>> +int arch_setup_runstate_guest(struct vcpu *v,
>> +                            struct vcpu_register_runstate_memory_area area);
> 
> NIT: code style, the indentation is off

Ok

> 
> 
>> +void arch_cleanup_runstate_guest(struct vcpu *v);
>> +
>> int arch_domain_create(struct domain *d,
>>                        struct xen_domctl_createdomain *config);
>> 
>> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
>> index ac53519d7f..fac030fb83 100644
>> --- a/xen/include/xen/sched.h
>> +++ b/xen/include/xen/sched.h
>> @@ -29,11 +29,6 @@
>> #include <public/vcpu.h>
>> #include <public/event_channel.h>
>> 
>> -#ifdef CONFIG_COMPAT
>> -#include <compat/vcpu.h>
>> -DEFINE_XEN_GUEST_HANDLE(vcpu_runstate_info_compat_t);
>> -#endif
>> -
>> /*
>>  * Stats
>>  *
>> @@ -166,16 +161,7 @@ struct vcpu
>>     struct sched_unit *sched_unit;
>> 
>>     struct vcpu_runstate_info runstate;
>> -#ifndef CONFIG_COMPAT
>> -# define runstate_guest(v) ((v)->runstate_guest)
>> -    XEN_GUEST_HANDLE(vcpu_runstate_info_t) runstate_guest; /* guest address */
>> -#else
>> -# define runstate_guest(v) ((v)->runstate_guest.native)
>> -    union {
>> -        XEN_GUEST_HANDLE(vcpu_runstate_info_t) native;
>> -        XEN_GUEST_HANDLE(vcpu_runstate_info_compat_t) compat;
>> -    } runstate_guest; /* guest address */
>> -#endif
>> +
>>     unsigned int     new_state;
>> 
>>     /* Has the FPU been initialised? */
>> -- 
>> 2.17.1