[PATCH] Revert "xen/x86: Workaround 64-bit hypervisor and 32-bitinitial domain." and "xen/x86: Use memblock_reserve forsensitive areas."

[Konrad Rzeszutek Wilk]

This reverts commit 806c312e50f122c47913145cf884f53dd09d9199 and
commit 59b294403e9814e7c1154043567f0d71bac7a511.

And also documents setup.c and why we want to do it that way, which
is that we tried to make the the memblock_reserve more selective so
that it would be clear what region is reserved. Sadly we ran
in the problem wherein on a 64-bit hypervisor with a 32-bit
initial domain, the pt_base has the cr3 value which is not
neccessarily where the pagetable starts! As Jan put it: "
Actually, the adjustment turns out to be correct: The page
tables for a 32-on-64 dom0 get allocated in the order "first L1",
"first L2", "first L3", so the offset to the page table base is
indeed 2. When reading xen/include/public/xen.h's comment
very strictly, this is not a violation (since there nothing is said
that the first thing in the page table space is pointed to by
pt_base; I admit that this seems to be implied though, namely
do I think that it is implied that the page table space is the
range [pt_base, pt_base + nt_pt_frames), whereas that
range here indeed is [pt_base - 2, pt_base - 2 + nt_pt_frames),
which - without a priori knowledge - the kernel would have
difficulty to figure out)." - so lets just fall back to the
easy way and reserve the whole region.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/enlighten.c |   60 ----------------------------------------------
 arch/x86/xen/p2m.c       |    5 ----
 arch/x86/xen/setup.c     |   27 ++++++++++++++++++++
 3 files changed, 27 insertions(+), 65 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c1e940d..d87a038 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -998,66 +998,7 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
 
 	return ret;
 }
-/*
- * If the MFN is not in the m2p (provided to us by the hypervisor) this
- * function won't do anything. In practice this means that the XenBus
- * MFN won't be available for the initial domain. */
-static unsigned long __init xen_reserve_mfn(unsigned long mfn)
-{
-	unsigned long pfn, end_pfn = 0;
-
-	if (!mfn)
-		return end_pfn;
-
-	pfn = mfn_to_pfn(mfn);
-	if (phys_to_machine_mapping_valid(pfn)) {
-		end_pfn = PFN_PHYS(pfn) + PAGE_SIZE;
-		memblock_reserve(PFN_PHYS(pfn), end_pfn);
-	}
-	return end_pfn;
-}
-static void __init xen_reserve_internals(void)
-{
-	unsigned long size;
-	unsigned long last_phys = 0;
-
-	if (!xen_pv_domain())
-		return;
-
-	/* xen_start_info does not exist in the M2P, hence can't use
-	 * xen_reserve_mfn. */
-	memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
-	last_phys = __pa(xen_start_info) + PAGE_SIZE;
-
-	last_phys = max(xen_reserve_mfn(PFN_DOWN(xen_start_info->shared_info)), last_phys);
-	last_phys = max(xen_reserve_mfn(xen_start_info->store_mfn), last_phys);
 
-	if (!xen_initial_domain())
-		last_phys = max(xen_reserve_mfn(xen_start_info->console.domU.mfn), last_phys);
-
-	if (xen_feature(XENFEAT_auto_translated_physmap))
-		return;
-
-	/*
-	 * ALIGN up to compensate for the p2m_page pointing to an array that
-	 * can partially filled (look in xen_build_dynamic_phys_to_machine).
-	 */
-
-	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
-
-	/* We could use xen_reserve_mfn here, but would end up looping quite
-	 * a lot (and call memblock_reserve for each PAGE), so lets just use
-	 * the easy way and reserve it wholesale. */
-	memblock_reserve(__pa(xen_start_info->mfn_list), size);
-	last_phys = max(__pa(xen_start_info->mfn_list) + size, last_phys);
-	/* The pagetables are reserved in mmu.c */
-
-	/* Under 64-bit hypervisor with a 32-bit domain, the hypervisor
-	 * offsets the pt_base by two pages. Hence the reservation that is done
-	 * in mmu.c misses two pages. We correct it here if we detect this. */
-	if (last_phys < __pa(xen_start_info->pt_base))
-		memblock_reserve(last_phys, __pa(xen_start_info->pt_base) - last_phys);
-}
 void xen_setup_shared_info(void)
 {
 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
@@ -1418,7 +1359,6 @@ asmlinkage void __init xen_start_kernel(void)
 	xen_raw_console_write("mapping kernel into physical memory\n");
 	xen_setup_kernel_pagetable((pgd_t *)xen_start_info->pt_base, xen_start_info->nr_pages);
 
-	xen_reserve_internals();
 	/* Allocate and initialize top and mid mfn levels for p2m structure */
 	xen_build_mfn_list_list();
 
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 95c3ea2..c3e9291 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -388,11 +388,6 @@ void __init xen_build_dynamic_phys_to_machine(void)
 	}
 
 	m2p_override_init();
-
-	/* NOTE: We cannot call memblock_reserve here for the mfn_list as there
-	 * isn't enough pieces to make it work (for one - we are still using the
-	 * Xen provided pagetable). Do it later in xen_reserve_internals.
-	 */
 }
 #ifdef CONFIG_X86_64
 #include <linux/bootmem.h>
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 9efca75..740517b 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -424,6 +424,33 @@ char * __init xen_memory_setup(void)
 	e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
 			E820_RESERVED);
 
+	/*
+	 * Reserve Xen bits:
+	 *  - mfn_list
+	 *  - xen_start_info
+	 * See comment above "struct start_info" in <xen/interface/xen.h>
+	 * We tried to make the the memblock_reserve more selective so
+	 * that it would be clear what region is reserved. Sadly we ran
+	 * in the problem wherein on a 64-bit hypervisor with a 32-bit
+	 * initial domain, the pt_base has the cr3 value which is not
+	 * neccessarily where the pagetable starts! As Jan put it: "
+	 * Actually, the adjustment turns out to be correct: The page
+	 * tables for a 32-on-64 dom0 get allocated in the order "first L1",
+	 * "first L2", "first L3", so the offset to the page table base is
+	 * indeed 2. When reading xen/include/public/xen.h's comment
+	 * very strictly, this is not a violation (since there nothing is said
+	 * that the first thing in the page table space is pointed to by
+	 * pt_base; I admit that this seems to be implied though, namely
+	 * do I think that it is implied that the page table space is the
+	 * range [pt_base, pt_base + nt_pt_frames), whereas that
+	 * range here indeed is [pt_base - 2, pt_base - 2 + nt_pt_frames),
+	 * which - without a priori knowledge - the kernel would have
+	 * difficulty to figure out)." - so lets just fall back to the
+	 * easy way and reserve the whole region.
+	 */
+	memblock_reserve(__pa(xen_start_info->mfn_list),
+			 xen_start_info->pt_base - xen_start_info->mfn_list);
+
 	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
 	return "Xen";
-- 
1.7.7.6

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