Mailing List Archive

xen/arch/x86/hvm/hvm.c | 54 +++++++++++++++++++++++++++------------
xen/arch/x86/hvm/svm/nestedsvm.c | 6 ----
xen/arch/x86/hvm/vmx/vvmx.c | 11 +------
3 files changed, 39 insertions(+), 32 deletions(-)


The nested hvm code maps pages of the guest hvm. These maps live beyond
a hypervisor entry/exit pair, and thus their liveness cannot be ensured
with get_gfn/put_gfn critical sections. Ensure their liveness by
increasing the page ref count, instead.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>

diff -r 7b6db593bda0 -r 4e0c533a3e1d xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1801,12 +1801,16 @@ int hvm_virtual_to_linear_addr(
return 0;
}

-/* We leave this function holding a lock on the p2m entry */
+/* On non-NULL return, we leave this function holding an additional
+ * ref on the underlying mfn, if any */
static void *__hvm_map_guest_frame(unsigned long gfn, bool_t writable)
{
+ void *map;
unsigned long mfn;
p2m_type_t p2mt;
+ struct page_info *pg;
struct domain *d = current->domain;
+ int rc;

mfn = mfn_x(writable
? get_gfn_unshare(d, gfn, &p2mt)
@@ -1828,7 +1832,21 @@ static void *__hvm_map_guest_frame(unsig
if ( writable )
paging_mark_dirty(d, mfn);

- return map_domain_page(mfn);
+ /* Get a ref on the page, considering that it could be shared */
+ pg = mfn_to_page(mfn);
+ rc = get_page(pg, d);
+ if ( !rc && !writable )
+ /* Page could be shared */
+ rc = get_page(pg, dom_cow);
+ if ( !rc )
+ {
+ put_gfn(d, gfn);
+ return NULL;
+ }
+
+ map = map_domain_page(mfn);
+ put_gfn(d, gfn);
+ return map;
}

void *hvm_map_guest_frame_rw(unsigned long gfn)
@@ -1844,11 +1862,16 @@ void *hvm_map_guest_frame_ro(unsigned lo
void hvm_unmap_guest_frame(void *p)
{
if ( p )
+ {
+ unsigned long mfn = xen_map_to_mfn(p);
unmap_domain_page(p);
+ put_page(mfn_to_page(mfn));
+ }
}

-static void *hvm_map_entry(unsigned long va, unsigned long *gfn)
+static void *hvm_map_entry(unsigned long va)
{
+ unsigned long gfn;
uint32_t pfec;
char *v;

@@ -1865,11 +1888,11 @@ static void *hvm_map_entry(unsigned long
* treat it as a kernel-mode read (i.e. no access checks).
*/
pfec = PFEC_page_present;
- *gfn = paging_gva_to_gfn(current, va, &pfec);
+ gfn = paging_gva_to_gfn(current, va, &pfec);
if ( (pfec == PFEC_page_paged) || (pfec == PFEC_page_shared) )
goto fail;

- v = hvm_map_guest_frame_rw(*gfn);
+ v = hvm_map_guest_frame_rw(gfn);
if ( v == NULL )
goto fail;

@@ -1880,11 +1903,9 @@ static void *hvm_map_entry(unsigned long
return NULL;
}

-static void hvm_unmap_entry(void *p, unsigned long gfn)
+static void hvm_unmap_entry(void *p)
{
hvm_unmap_guest_frame(p);
- if ( p && (gfn != INVALID_GFN) )
- put_gfn(current->domain, gfn);
}

static int hvm_load_segment_selector(
@@ -1896,7 +1917,6 @@ static int hvm_load_segment_selector(
int fault_type = TRAP_invalid_tss;
struct cpu_user_regs *regs = guest_cpu_user_regs();
struct vcpu *v = current;
- unsigned long pdesc_gfn = INVALID_GFN;

if ( regs->eflags & X86_EFLAGS_VM )
{
@@ -1930,7 +1950,7 @@ static int hvm_load_segment_selector(
if ( ((sel & 0xfff8) + 7) > desctab.limit )
goto fail;

- pdesc = hvm_map_entry(desctab.base + (sel & 0xfff8), &pdesc_gfn);
+ pdesc = hvm_map_entry(desctab.base + (sel & 0xfff8));
if ( pdesc == NULL )
goto hvm_map_fail;

@@ -1990,7 +2010,7 @@ static int hvm_load_segment_selector(
desc.b |= 0x100;

skip_accessed_flag:
- hvm_unmap_entry(pdesc, pdesc_gfn);
+ hvm_unmap_entry(pdesc);

segr.base = (((desc.b << 0) & 0xff000000u) |
((desc.b << 16) & 0x00ff0000u) |
@@ -2006,7 +2026,7 @@ static int hvm_load_segment_selector(
return 0;

unmap_and_fail:
- hvm_unmap_entry(pdesc, pdesc_gfn);
+ hvm_unmap_entry(pdesc);
fail:
hvm_inject_exception(fault_type, sel & 0xfffc, 0);
hvm_map_fail:
@@ -2021,7 +2041,7 @@ void hvm_task_switch(
struct cpu_user_regs *regs = guest_cpu_user_regs();
struct segment_register gdt, tr, prev_tr, segr;
struct desc_struct *optss_desc = NULL, *nptss_desc = NULL, tss_desc;
- unsigned long eflags, optss_gfn = INVALID_GFN, nptss_gfn = INVALID_GFN;
+ unsigned long eflags;
int exn_raised, rc;
struct {
u16 back_link,__blh;
@@ -2047,11 +2067,11 @@ void hvm_task_switch(
goto out;
}

- optss_desc = hvm_map_entry(gdt.base + (prev_tr.sel & 0xfff8), &optss_gfn);
+ optss_desc = hvm_map_entry(gdt.base + (prev_tr.sel & 0xfff8));
if ( optss_desc == NULL )
goto out;

- nptss_desc = hvm_map_entry(gdt.base + (tss_sel & 0xfff8), &nptss_gfn);
+ nptss_desc = hvm_map_entry(gdt.base + (tss_sel & 0xfff8));
if ( nptss_desc == NULL )
goto out;

@@ -2216,8 +2236,8 @@ void hvm_task_switch(
}

out:
- hvm_unmap_entry(optss_desc, optss_gfn);
- hvm_unmap_entry(nptss_desc, nptss_gfn);
+ hvm_unmap_entry(optss_desc);
+ hvm_unmap_entry(nptss_desc);
}

#define HVMCOPY_from_guest (0u<<0)
diff -r 7b6db593bda0 -r 4e0c533a3e1d xen/arch/x86/hvm/svm/nestedsvm.c
--- a/xen/arch/x86/hvm/svm/nestedsvm.c
+++ b/xen/arch/x86/hvm/svm/nestedsvm.c
@@ -81,10 +81,6 @@ int nestedsvm_vmcb_map(struct vcpu *v, u
if (nv->nv_vvmcx == NULL)
return 0;
nv->nv_vvmcxaddr = vmcbaddr;
- /* put_gfn here even though the map survives beyond this caller.
- * The map can likely survive beyond a hypervisor exit, thus we
- * need to put the gfn */
- put_gfn(current->domain, vmcbaddr >> PAGE_SHIFT);
}

return 1;
@@ -358,7 +354,6 @@ static int nsvm_vmrun_permissionmap(stru
ioport_80 = test_bit(0x80, ns_viomap);
ioport_ed = test_bit(0xed, ns_viomap);
hvm_unmap_guest_frame(ns_viomap);
- put_gfn(current->domain, svm->ns_iomap_pa >> PAGE_SHIFT);

svm->ns_iomap = nestedhvm_vcpu_iomap_get(ioport_80, ioport_ed);

@@ -889,7 +884,6 @@ nsvm_vmcb_guest_intercepts_ioio(paddr_t

enabled = test_bit(port, io_bitmap);
hvm_unmap_guest_frame(io_bitmap);
- put_gfn(current->domain, gfn);

if (!enabled)
return NESTEDHVM_VMEXIT_HOST;
diff -r 7b6db593bda0 -r 4e0c533a3e1d xen/arch/x86/hvm/vmx/vvmx.c
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -560,10 +560,7 @@ static void __map_io_bitmap(struct vcpu
if (nvmx->iobitmap[index])
hvm_unmap_guest_frame (nvmx->iobitmap[index]);
gpa = __get_vvmcs(vcpu_nestedhvm(v).nv_vvmcx, vmcs_reg);
- nvmx->iobitmap[index] = hvm_map_guest_frame_ro (gpa >> PAGE_SHIFT);
- /* See comment in nestedsvm_vmcb_map re putting this gfn and
- * liveness of the map it backs */
- put_gfn(current->domain, gpa >> PAGE_SHIFT);
+ nvmx->iobitmap[index] = hvm_map_guest_frame_ro(gpa >> PAGE_SHIFT);
}

static inline void map_io_bitmap_all(struct vcpu *v)
@@ -1138,12 +1135,9 @@ int nvmx_handle_vmptrld(struct cpu_user_

if ( nvcpu->nv_vvmcxaddr == VMCX_EADDR )
{
- nvcpu->nv_vvmcx = hvm_map_guest_frame_rw (gpa >> PAGE_SHIFT);
+ nvcpu->nv_vvmcx = hvm_map_guest_frame_rw(gpa >> PAGE_SHIFT);
nvcpu->nv_vvmcxaddr = gpa;
map_io_bitmap_all (v);
- /* See comment in nestedsvm_vmcb_map regarding putting this
- * gfn and liveness of the map that uses it */
- put_gfn(current->domain, gpa >> PAGE_SHIFT);
}

vmreturn(regs, VMSUCCEED);
@@ -1205,7 +1199,6 @@ int nvmx_handle_vmclear(struct cpu_user_
if ( vvmcs )
__set_vvmcs(vvmcs, NVMX_LAUNCH_STATE, 0);
hvm_unmap_guest_frame(vvmcs);
- put_gfn(current->domain, gpa >> PAGE_SHIFT);
}

vmreturn(regs, VMSUCCEED);

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