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Re: [PATCH 2/2] x86/mm: correct PG_log_dirty definition
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Wed, 6 Aug 2025 17:24:05 -0400
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Penny Zheng <Penny.Zheng@xxxxxxx>
- Delivery-date: Wed, 06 Aug 2025 21:24:39 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-08-05 03:59, Jan Beulich wrote:
While it is correct that in shim-exclusive mode log-dirty handling is
all unreachable code, the present conditional still isn't correct: In a
HVM=n and SHADOW_PAGING=n configuration log-dirty code also is all
unreachable (and hence violating Misra rule 2.1).
As we're aiming at moving away from special casing PV_SHIM_EXCLUSIVE=y,
don't retain that part of the conditional.
Because of hypercall-defs.c we need to carry out the dependency by
introducing a new auxiliary PAGING control.
Since compiling out mm/paging.c altogether would entail further changes,
merely conditionalize the one function in there (paging_enable()) which
would otherwise remain unreachable (Misra rule 2.1 again) when PAGING=n.
Fixes: 23d4e0d17b76 ("x86/shim: fix build with PV_SHIM_EXCLUSIVE and
SHADOW_PAGING")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Of course PAGING is at risk of being confused with MEM_PAGING. It not
having a prompt, I hope that's tolerable, as I can't really think of a
better name.
Other PG_log_dirty pre-processor conditionals then likely also want
replacing. mm/paging.c and mm/p2m-basic.c could also be compiled out
altogether when PAGING=n, at the expense of introducing a few more
stubs.
FTAOD, the Fixes: tag being referenced does not mean this patch corrects
the far more recently introduced build issue with the combination of the
two features. That's still work that I expect Penny to carry out (with
there still being the option of reverting the final part of the earlier
series).
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -864,6 +864,7 @@ void paging_final_teardown(struct domain
p2m_final_teardown(d);
}
+#ifdef CONFIG_PAGING
The file already has a lot of uses of #if PG_log_dirty with similar
meaning, if I am not mistaken, so using that would make it more
consistent. But CONFIG_PAGING is directly tied to the Kconfig, so maybe
it is better? Just something I noticed.
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Regards,
Jason
/* Enable an arbitrary paging-assistance mode. Call once at domain
* creation. */
int paging_enable(struct domain *d, u32 mode)
@@ -889,6 +890,7 @@ int paging_enable(struct domain *d, u32
else
return shadow_enable(d, mode);
}
+#endif
#ifdef CONFIG_HVM
/* Called from the guest to indicate that a process is being torn down
|
