Re: [PATCH v2 4/7] x86/xen: support nested lazy_mmu sections (again)

Jürgen Groß
2025-09-09T09:42:05Z

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On 08.09.25 09:39, Kevin Brodsky wrote:
> Commit 49147beb0ccb ("x86/xen: allow nesting of same lazy mode")
> originally introduced support for nested lazy sections (LAZY_MMU and
> LAZY_CPU). It later got reverted by commit c36549ff8d84 as its
> implementation turned out to be intolerant to preemption.
>
> Now that the lazy_mmu API allows enter() to pass through a state to
> the matching leave() call, we can support nesting again for the
> LAZY_MMU mode in a preemption-safe manner. If xen_enter_lazy_mmu() is
> called inside an active lazy_mmu section, xen_lazy_mode will already
> be set to XEN_LAZY_MMU and we can then return LAZY_MMU_NESTED to
> instruct the matching xen_leave_lazy_mmu() call to leave
> xen_lazy_mode unchanged.
>
> The only effect of this patch is to ensure that xen_lazy_mode
> remains set to XEN_LAZY_MMU until the outermost lazy_mmu section
> ends. xen_leave_lazy_mmu() still calls xen_mc_flush()
> unconditionally.
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>

Reviewed-by: Juergen Gross <jgross@suse.com>

Juergen

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