[xen staging] xen/domain: Add vmtrace_size domain creation parameter

[patchbot@xxxxxxx]

commit 217dd79ee29286b85074d22cc75ee064206fb2af
Author:     MichaÅ? LeszczyÅ?ski <michal.leszczynski@xxxxxxx>
AuthorDate: Fri Jul 3 01:16:10 2020 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Feb 5 17:37:27 2021 +0000

    xen/domain: Add vmtrace_size domain creation parameter
    
    To use vmtrace, buffers of a suitable size need allocating, and different
    tasks will want different sizes.
    
    Add a domain creation parameter, and audit it appropriately in the
    {arch_,}sanitise_domain_config() functions.
    
    For now, the x86 specific auditing is tuned to Processor Trace running in
    Single Output mode, which requires a single contiguous range of memory.
    
    The size is given an arbitrary limit of 64M which is expected to be enough 
for
    anticipated usecases, but not large enough to get into 
long-running-hypercall
    problems.
    
    Signed-off-by: MichaÅ? LeszczyÅ?ski <michal.leszczynski@xxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 xen/arch/x86/domain.c       | 23 ++++++++++++++
 xen/common/domain.c         | 77 +++++++++++++++++++++++++++++++++++++++++++++
 xen/include/public/domctl.h |  3 ++
 xen/include/xen/sched.h     |  6 ++++
 4 files changed, 109 insertions(+)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index b9ba04633e..6c7ee25f3b 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -660,6 +660,29 @@ int arch_sanitise_domain_config(struct 
xen_domctl_createdomain *config)
         return -EINVAL;
     }
 
+    if ( config->vmtrace_size )
+    {
+        unsigned int size = config->vmtrace_size;
+
+        ASSERT(vmtrace_available); /* Checked by common code. */
+
+        /*
+         * For now, vmtrace is restricted to HVM guests, and using a
+         * power-of-2 buffer between 4k and 64M in size.
+         */
+        if ( !hvm )
+        {
+            dprintk(XENLOG_INFO, "vmtrace not supported for PV\n");
+            return -EINVAL;
+        }
+
+        if ( size < PAGE_SIZE || size > MB(64) || (size & (size - 1)) )
+        {
+            dprintk(XENLOG_INFO, "Unsupported vmtrace size: %#x\n", size);
+            return -EINVAL;
+        }
+    }
+
     return 0;
 }
 
diff --git a/xen/common/domain.c b/xen/common/domain.c
index d1e94d88cf..d85984638a 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -132,6 +132,69 @@ static void vcpu_info_reset(struct vcpu *v)
     v->vcpu_info_mfn = INVALID_MFN;
 }
 
+static void vmtrace_free_buffer(struct vcpu *v)
+{
+    const struct domain *d = v->domain;
+    struct page_info *pg = v->vmtrace.pg;
+    unsigned int i;
+
+    if ( !pg )
+        return;
+
+    v->vmtrace.pg = NULL;
+
+    for ( i = 0; i < (d->vmtrace_size >> PAGE_SHIFT); i++ )
+    {
+        put_page_alloc_ref(&pg[i]);
+        put_page_and_type(&pg[i]);
+    }
+}
+
+static int vmtrace_alloc_buffer(struct vcpu *v)
+{
+    struct domain *d = v->domain;
+    struct page_info *pg;
+    unsigned int i;
+
+    if ( !d->vmtrace_size )
+        return 0;
+
+    pg = alloc_domheap_pages(d, get_order_from_bytes(d->vmtrace_size),
+                             MEMF_no_refcount);
+    if ( !pg )
+        return -ENOMEM;
+
+    for ( i = 0; i < (d->vmtrace_size >> PAGE_SHIFT); i++ )
+        if ( unlikely(!get_page_and_type(&pg[i], d, PGT_writable_page)) )
+            /*
+             * The domain can't possibly know about this page yet, so failure
+             * here is a clear indication of something fishy going on.
+             */
+            goto refcnt_err;
+
+    /*
+     * We must only let vmtrace_free_buffer() take any action in the success
+     * case when we've taken all the refs it intends to drop.
+     */
+    v->vmtrace.pg = pg;
+    return 0;
+
+ refcnt_err:
+    /*
+     * We can theoretically reach this point if someone has taken 2^43 refs on
+     * the frames in the time the above loop takes to execute, or someone has
+     * made a blind decrease reservation hypercall and managed to pick the
+     * right mfn.  Free the memory we safely can, and leak the rest.
+     */
+    while ( i-- )
+    {
+        put_page_alloc_ref(&pg[i]);
+        put_page_and_type(&pg[i]);
+    }
+
+    return -ENODATA;
+}
+
 /*
  * Release resources held by a vcpu.  There may or may not be live references
  * to the vcpu, and it may or may not be fully constructed.
@@ -140,6 +203,8 @@ static void vcpu_info_reset(struct vcpu *v)
  */
 static int vcpu_teardown(struct vcpu *v)
 {
+    vmtrace_free_buffer(v);
+
     return 0;
 }
 
@@ -201,6 +266,9 @@ struct vcpu *vcpu_create(struct domain *d, unsigned int 
vcpu_id)
     if ( sched_init_vcpu(v) != 0 )
         goto fail_wq;
 
+    if ( vmtrace_alloc_buffer(v) != 0 )
+        goto fail_wq;
+
     if ( arch_vcpu_create(v) != 0 )
         goto fail_sched;
 
@@ -449,6 +517,12 @@ static int sanitise_domain_config(struct 
xen_domctl_createdomain *config)
         }
     }
 
+    if ( config->vmtrace_size && !vmtrace_available )
+    {
+        dprintk(XENLOG_INFO, "vmtrace requested but not available\n");
+        return -EINVAL;
+    }
+
     return arch_sanitise_domain_config(config);
 }
 
@@ -474,7 +548,10 @@ struct domain *domain_create(domid_t domid,
     ASSERT(is_system_domain(d) ? config == NULL : config != NULL);
 
     if ( config )
+    {
         d->options = config->flags;
+        d->vmtrace_size = config->vmtrace_size;
+    }
 
     /* Sort out our idea of is_control_domain(). */
     d->is_privileged = is_priv;
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 666aeb71bf..88a5b1ef5d 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -95,6 +95,9 @@ struct xen_domctl_createdomain {
     int32_t max_grant_frames;
     int32_t max_maptrack_frames;
 
+    /* Per-vCPU buffer size in bytes.  0 to disable. */
+    uint32_t vmtrace_size;
+
     struct xen_arch_domainconfig arch;
 };
 
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 06dba1a397..bc78a09a53 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -272,6 +272,10 @@ struct vcpu
     /* vPCI per-vCPU area, used to store data for long running operations. */
     struct vpci_vcpu vpci;
 
+    struct {
+        struct page_info *pg; /* One contiguous allocation of d->vmtrace_size 
*/
+    } vmtrace;
+
     struct arch_vcpu arch;
 
 #ifdef CONFIG_IOREQ_SERVER
@@ -547,6 +551,8 @@ struct domain
         unsigned int guest_request_sync          : 1;
     } monitor;
 
+    unsigned int vmtrace_size; /* Buffer size in bytes, or 0 to disable. */
+
 #ifdef CONFIG_ARGO
     /* Argo interdomain communication support */
     struct argo_domain *argo;
--
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