While looking at the origin of very frequently executed hypercalls I
realized that the high page accessor functions in Linux would be good
candidates to handle in the hypervisor - clearing or copying to/from
a high page is a pretty frequent operation (provided there's enough
memory in the domain). While prior to the first submission I only
measured kernel builds (where the results are not hinting at a
meaningful improvement), I now found time to do a more specific
analysis: page clearing is being improved by about 20%, page copying
doesn't seem to significantly benefit (though that may be an effect of
the simplistic copy_page() implementation Xen currently uses) -
nevertheless I would think that if one function is supported by the
hypervisor, then the other should also be.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Index: 2008-10-27/xen/arch/x86/mm.c
===================================================================
--- 2008-10-27.orig/xen/arch/x86/mm.c 2008-10-27 11:11:36.000000000 +0100
+++ 2008-10-27/xen/arch/x86/mm.c 2008-10-27 11:11:52.000000000 +0100
@@ -2431,6 +2431,29 @@ static inline cpumask_t vcpumask_to_pcpu
return pmask;
}
+#ifdef __i386__
+static inline void *fixmap_domain_page(unsigned long mfn)
+{
+ unsigned int cpu = smp_processor_id();
+ void *ptr = (void *)fix_to_virt(FIX_PAE_HIGHMEM_0 + cpu);
+
+ l1e_write(fix_pae_highmem_pl1e - cpu,
+ l1e_from_pfn(mfn, __PAGE_HYPERVISOR));
+ flush_tlb_one_local(ptr);
+ return ptr;
+}
+static inline void fixunmap_domain_page(const void *ptr)
+{
+ unsigned int cpu = virt_to_fix((unsigned long)ptr) - FIX_PAE_HIGHMEM_0;
+
+ l1e_write(fix_pae_highmem_pl1e - cpu, l1e_empty());
+ this_cpu(make_cr3_timestamp) = this_cpu(tlbflush_time);
+}
+#else
+#define fixmap_domain_page(mfn) mfn_to_virt(mfn)
+#define fixunmap_domain_page(ptr) ((void)(ptr))
+#endif
+
int do_mmuext_op(
XEN_GUEST_HANDLE(mmuext_op_t) uops,
unsigned int count,
@@ -2700,6 +2723,66 @@ int do_mmuext_op(
break;
}
+ case MMUEXT_CLEAR_PAGE:
+ {
+ unsigned char *ptr;
+
+ okay = !get_page_and_type_from_pagenr(mfn, PGT_writable_page,
+ FOREIGNDOM, 0);
+ if ( unlikely(!okay) )
+ {
+ MEM_LOG("Error while clearing mfn %lx", mfn);
+ break;
+ }
+
+ /* A page is dirtied when it's being cleared. */
+ paging_mark_dirty(d, mfn);
+
+ ptr = fixmap_domain_page(mfn);
+ clear_page(ptr);
+ fixunmap_domain_page(ptr);
+
+ put_page_and_type(page);
+ break;
+ }
+
+ case MMUEXT_COPY_PAGE:
+ {
+ const unsigned char *src;
+ unsigned char *dst;
+ unsigned long src_mfn;
+
+ src_mfn = gmfn_to_mfn(FOREIGNDOM, op.arg2.src_mfn);
+ okay = get_page_from_pagenr(src_mfn, FOREIGNDOM);
+ if ( unlikely(!okay) )
+ {
+ MEM_LOG("Error while copying from mfn %lx", src_mfn);
+ break;
+ }
+
+ okay = !get_page_and_type_from_pagenr(mfn, PGT_writable_page,
+ FOREIGNDOM, 0);
+ if ( unlikely(!okay) )
+ {
+ put_page(mfn_to_page(src_mfn));
+ MEM_LOG("Error while copying to mfn %lx", mfn);
+ break;
+ }
+
+ /* A page is dirtied when it's being copied to. */
+ paging_mark_dirty(d, mfn);
+
+ src = map_domain_page(src_mfn);
+ dst = fixmap_domain_page(mfn);
+ copy_page(dst, src);
+ fixunmap_domain_page(dst);
+ unmap_domain_page(src);
+
+ put_page_and_type(page);
+ put_page(mfn_to_page(src_mfn));
+ break;
+ }
+
default:
MEM_LOG("Invalid extended pt command 0x%x", op.cmd);
rc = -ENOSYS;
Index: 2008-10-27/xen/arch/x86/x86_64/compat/mm.c
===================================================================
--- 2008-10-27.orig/xen/arch/x86/x86_64/compat/mm.c 2008-10-27
11:22:56.000000000 +0100
+++ 2008-10-27/xen/arch/x86/x86_64/compat/mm.c 2008-10-27 11:11:52.000000000
+0100
@@ -231,6 +231,8 @@ int compat_mmuext_op(XEN_GUEST_HANDLE(mm
case MMUEXT_PIN_L4_TABLE:
case MMUEXT_UNPIN_TABLE:
case MMUEXT_NEW_BASEPTR:
+ case MMUEXT_CLEAR_PAGE:
+ case MMUEXT_COPY_PAGE:
arg1 = XLAT_mmuext_op_arg1_mfn;
break;
default:
@@ -258,6 +260,9 @@ int compat_mmuext_op(XEN_GUEST_HANDLE(mm
case MMUEXT_INVLPG_MULTI:
arg2 = XLAT_mmuext_op_arg2_vcpumask;
break;
+ case MMUEXT_COPY_PAGE:
+ arg2 = XLAT_mmuext_op_arg2_src_mfn;
+ break;
default:
arg2 = -1;
break;
Index: 2008-10-27/xen/common/kernel.c
===================================================================
--- 2008-10-27.orig/xen/common/kernel.c 2008-10-17 08:29:02.000000000 +0200
+++ 2008-10-27/xen/common/kernel.c 2008-10-27 11:25:15.000000000 +0100
@@ -221,7 +221,8 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDL
fi.submap |= 1U << XENFEAT_supervisor_mode_kernel;
#ifdef CONFIG_X86
if ( !is_hvm_vcpu(current) )
- fi.submap |= 1U << XENFEAT_mmu_pt_update_preserve_ad;
+ fi.submap |= (1U << XENFEAT_mmu_pt_update_preserve_ad) |
+ (1U << XENFEAT_highmem_assist);
#endif
break;
default:
Index: 2008-10-27/xen/include/public/features.h
===================================================================
--- 2008-10-27.orig/xen/include/public/features.h 2008-01-17
09:25:56.000000000 +0100
+++ 2008-10-27/xen/include/public/features.h 2008-10-27 11:24:26.000000000
+0100
@@ -59,6 +59,9 @@
/* x86: Does this Xen host support the MMU_PT_UPDATE_PRESERVE_AD hypercall? */
#define XENFEAT_mmu_pt_update_preserve_ad 5
+/* x86: Does this Xen host support the MMU_{CLEAR,COPY}_PAGE hypercall? */
+#define XENFEAT_highmem_assist 6
+
#define XENFEAT_NR_SUBMAPS 1
#endif /* __XEN_PUBLIC_FEATURES_H__ */
Index: 2008-10-27/xen/include/public/xen.h
===================================================================
--- 2008-10-27.orig/xen/include/public/xen.h 2008-10-27 11:22:56.000000000
+0100
+++ 2008-10-27/xen/include/public/xen.h 2008-10-27 11:11:52.000000000 +0100
@@ -231,6 +231,13 @@ DEFINE_XEN_GUEST_HANDLE(xen_pfn_t);
* cmd: MMUEXT_SET_LDT
* linear_addr: Linear address of LDT base (NB. must be page-aligned).
* nr_ents: Number of entries in LDT.
+ *
+ * cmd: MMUEXT_CLEAR_PAGE
+ * mfn: Machine frame number to be cleared.
+ *
+ * cmd: MMUEXT_COPY_PAGE
+ * mfn: Machine frame number of the destination page.
+ * src_mfn: Machine frame number of the source page.
*/
#define MMUEXT_PIN_L1_TABLE 0
#define MMUEXT_PIN_L2_TABLE 1
@@ -247,12 +254,15 @@ DEFINE_XEN_GUEST_HANDLE(xen_pfn_t);
#define MMUEXT_FLUSH_CACHE 12
#define MMUEXT_SET_LDT 13
#define MMUEXT_NEW_USER_BASEPTR 15
+#define MMUEXT_CLEAR_PAGE 16
+#define MMUEXT_COPY_PAGE 17
#ifndef __ASSEMBLY__
struct mmuext_op {
unsigned int cmd;
union {
- /* [UN]PIN_TABLE, NEW_BASEPTR, NEW_USER_BASEPTR */
+ /* [UN]PIN_TABLE, NEW_BASEPTR, NEW_USER_BASEPTR
+ * CLEAR_PAGE, COPY_PAGE */
xen_pfn_t mfn;
/* INVLPG_LOCAL, INVLPG_ALL, SET_LDT */
unsigned long linear_addr;
@@ -266,6 +276,8 @@ struct mmuext_op {
#else
void *vcpumask;
#endif
+ /* COPY_PAGE */
+ xen_pfn_t src_mfn;
} arg2;
};
typedef struct mmuext_op mmuext_op_t;
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