[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v2 5/8] xen/riscv: introduce asm/pmap.h header



Hi,

On 22/07/2024 15:44, Oleksii Kurochko wrote:
On Mon, 2024-07-22 at 14:54 +0200, Jan Beulich wrote:
On 12.07.2024 18:22, Oleksii Kurochko wrote:
--- /dev/null
+++ b/xen/arch/riscv/include/asm/pmap.h
@@ -0,0 +1,28 @@
+#ifndef __ASM_PMAP_H__
+#define __ASM_PMAP_H__
+
+#include <xen/bug.h>
+#include <xen/mm.h>
+
+#include <asm/fixmap.h>
+
+static inline void arch_pmap_map(unsigned int slot, mfn_t mfn)
+{
+    pte_t *entry = &xen_fixmap[slot];
+    pte_t pte;
+
+    ASSERT(!pte_is_valid(*entry));
+
+    pte = mfn_to_xen_entry(mfn, PAGE_HYPERVISOR_RW);
+    pte.pte |= PTE_LEAF_DEFAULT;
+    write_pte(entry, pte);
+}
+
+static inline void arch_pmap_unmap(unsigned int slot)
+{
+    pte_t pte = {};
+
+    write_pte(&xen_fixmap[slot], pte);
+}

Why are these not using set_fixmap() / clear_fixmap() respectively?
They haven't been introduced yet. And I thought that these fucntion are
used only in pmap_{un}map() and that is the reason why I decided to not
introduce them. But while writing the answer on another comment, I
found other places where set_fixmap() / clear_fixmap() are used, so I
will introduce them and reuse here.

I am guessing you are going to implement set_fixmap()/clear_fixmap() using map_pages_to_xen(). If so, for early boot you are going to end up in a circular loop because map_pages_to_xen() will likely use pmap() which will call set_fixmap().

There is a big comment in common/pmap.c which explain why arch_pmap_* was introduced rather than calling *_fixmap() directly:

    /*
     * We cannot use set_fixmap() here. We use PMAP when the domain map
* page infrastructure is not yet initialized, so map_pages_to_xen() called * by set_fixmap() needs to map pages on demand, which then calls pmap() * again, resulting in a loop. Modify the PTEs directly instead. The same
     * is true for pmap_unmap().
     */

Cheers,

--
Julien Grall



 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.