[Public] Hi,
> -----Original Message----- > From: Jan Beulich <[email protected]> > Sent: Sunday, September 14, 2025 10:04 PM > To: Tamas K Lengyel <[email protected]>; Penny, Zheng > <[email protected]> > Cc: Huang, Ray <[email protected]>; Andrew Cooper > <[email protected]>; Roger Pau Monné <[email protected]>; > Alexandru Isaila <[email protected]>; Petre Pircalabu > <[email protected]>; Daniel P. Smith <[email protected]>; > [email protected] > Subject: Re: [PATCH v2 04/26] xen: consolidate CONFIG_VM_EVENT > > On 14.09.2025 01:31, Tamas K Lengyel wrote: > >>> @@ -99,10 +98,40 @@ long p2m_set_mem_access_multi(struct domain *d, > >>> int p2m_get_mem_access(struct domain *d, gfn_t gfn, xenmem_access_t > *access, > >>> unsigned int altp2m_idx); > >>> > >>> -#ifdef CONFIG_VM_EVENT > >>> int mem_access_memop(unsigned long cmd, > >>> XEN_GUEST_HANDLE_PARAM(xen_mem_access_op_t) > >>> arg); #else > >>> +static inline bool xenmem_access_to_p2m_access(const struct p2m_domain > *p2m, > >>> + xenmem_access_t xaccess, > >>> + p2m_access_t > >>> +*paccess) { > >>> + return false; > >>> +} > >> > >> So this is needed when VM_EVENT=n and ALTP2M=y. Tamas, is this a > >> configuration which makes sense? > > > > Yes, altp2m should be functional without vm_event being enabled. There > > could very well be in-guest only use of altp2m via #VE. This function > > is used in p2m_init_next_altp2m which means it being stubbed out like > > this when vm_event is disabled breaks altp2m. > > Oh, indeed - the stub still needs to handle XENMEM_access_default. Of course > with MEM_ACCESS=n it's not quite clear to me what p2m->default_access ought > to be; imo in principle that field ought to also go away in that case > (becoming hard- > coded p2m_access_rwx). While doing that will be a larger patch, perhaps using > the > hard-coded value here should be done right away. > > Once the code correctly handles MEM_ACCESS=n as an implication from > VM_EVENT=n, it's also questionable whether MEM_ACCESS_ALWAYS_ON > should be retained. > If we intend to remove MEM_ACCESS_ALWAYS_ON, I suggest to do the following modification on VM_EVENT to still keep y on default on x86: ``` diff --git a/xen/common/Kconfig b/xen/common/Kconfig index 7bd8a04730..61d48a5120 100644 --- a/xen/common/Kconfig +++ b/xen/common/Kconfig @@ -170,13 +170,10 @@ config HAS_VMAP config LIBFDT bool -config MEM_ACCESS_ALWAYS_ON - bool - config VM_EVENT - def_bool MEM_ACCESS_ALWAYS_ON - prompt "Memory Access and VM events" if !MEM_ACCESS_ALWAYS_ON + bool "Memory Access and VM events" depends on HVM + default X86 help Framework to configure memory access types for guests and receive ``` > Jan
