Re: [PATCH] adjust/fix LDT handling for Xen

[Jeremy Fitzhardinge]

Jan Beulich wrote:
> > > > Ingo Molnar <mingo@xxxxxxx> 14.01.08 16:48 >>>
> > > >         
> > * Jan Beulich <jbeulich@xxxxxxxxxx> wrote:
> >
> >     
> > > Don't rely on kmalloc(PAGE_SIZE) returning PAGE_SIZE aligned memory 
> > > (Xen requires GDT *and* LDT to be page-aligned). Using the page 
> > > allocator interface also removes the (albeit small) slab allocator 
> > > overhead. The same change being done for 64-bits for consistency.
> > >
> > > Further, the Xen hypercall interface expects the LDT address to be 
> > > virtual, not machine.
> > >       
> > coul dyou try this against x86.git as well? We already unified ldt.c as 
> > part of the paravirt patches.
> >     
>
> Sure, but it may take me a little while.

I've got the unified version here. 

Subject: xen: adjust/fix LDT handling for Xen

From: "Jan Beulich" <jbeulich@xxxxxxxxxx>

Don't rely on kmalloc(PAGE_SIZE) returning PAGE_SIZE aligned memory
(Xen requires GDT *and* LDT to be page-aligned). Using the page
allocator interface also removes the (albeit small) slab allocator
overhead. The same change being done for 64-bits for consistency.

Further, the Xen hypercall interface expects the LDT address to be
virtual, not machine.

[ Adjusted to unified ldt.c - Jeremy ]

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Acked-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>

---
arch/x86/kernel/ldt.c    |    7 +++----
arch/x86/xen/enlighten.c |    9 +--------
2 files changed, 4 insertions(+), 12 deletions(-)

===================================================================
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -12,7 +12,6 @@
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/vmalloc.h>
-#include <linux/slab.h>

#include <asm/uaccess.h>
#include <asm/system.h>
@@ -40,7 +39,7 @@ static int alloc_ldt(mm_context_t *pc, i
	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
	else
-		newldt = kmalloc(mincount * LDT_ENTRY_SIZE, GFP_KERNEL);
+		newldt = (void *)__get_free_page(GFP_KERNEL);

	if (!newldt)
		return -ENOMEM;
@@ -78,7 +77,7 @@ static int alloc_ldt(mm_context_t *pc, i
		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
			vfree(oldldt);
		else
-			kfree(oldldt);
+			put_page(virt_to_page(oldldt));
	}
	return 0;
}
@@ -129,7 +128,7 @@ void destroy_context(struct mm_struct *m
		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
			vfree(mm->context.ldt);
		else
-			kfree(mm->context.ldt);
+			put_page(virt_to_page(mm->context.ldt));
		mm->context.size = 0;
	}
}
===================================================================
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -275,19 +275,12 @@ static unsigned long xen_store_tr(void)

static void xen_set_ldt(const void *addr, unsigned entries)
{
-	unsigned long linear_addr = (unsigned long)addr;
	struct mmuext_op *op;
	struct multicall_space mcs = xen_mc_entry(sizeof(*op));

	op = mcs.args;
	op->cmd = MMUEXT_SET_LDT;
-	if (linear_addr) {
-		/* ldt my be vmalloced, use arbitrary_virt_to_machine */
-		xmaddr_t maddr;
-		maddr = arbitrary_virt_to_machine((unsigned long)addr);
-		linear_addr = (unsigned long)maddr.maddr;
-	}
-	op->arg1.linear_addr = linear_addr;
+	op->arg1.linear_addr = (unsigned long)addr;
	op->arg2.nr_ents = entries;

	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

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