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
