[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] tools: Mark ACPI SDTs as NVS in the PVH build path
On Tue Mar 11, 2025 at 8:30 AM GMT, Jan Beulich wrote: > On 10.03.2025 16:25, Alejandro Vallejo wrote: > > Commit cefeffc7e583 marked ACPI tables as NVS in the hvmloader path > > because SeaBIOS may otherwise just mark it as RAM. There is, however, > > yet another reason to do it even in the PVH path. Xen's incarnation of > > AML relies on having access to some ACPI tables (e.g: _STA of Processor > > objects relies on reading the processor online bit in its MADT entry) > > > > This is problematic if the OS tries to reclaim ACPI memory for page > > tables as it's needed for runtime and can't be reclaimed after the OSPM > > is up and running. > > > > Fixes: de6d188a519f("hvmloader: flip "ACPI data" to "ACPI NVS" type for > > ACPI table region)" > > Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx> > > --- > > I really, really, really dislike this idea of accessing the MADT from > > AML. > > I think this isn't Xen's invention, but something I've seen in various > systems' AML. > Do you mean ACPI hotplug? I don't think I've ever seen a real system with support for it. I don't suppose you remember any specifically? I'd be quite interested to have a look at their ACPI dumps. > > In time I'll try to implement something to stop doing it, but for > > the time being I find it preferable to align libxl to hvmloader rather > > than trying to restrict what's reclaimable and what isn't. > > --- > > tools/firmware/hvmloader/e820.c | 4 ++++ > > tools/libs/light/libxl_x86.c | 2 +- > > 2 files changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/tools/firmware/hvmloader/e820.c > > b/tools/firmware/hvmloader/e820.c > > index c490a0bc790c..86d39544e887 100644 > > --- a/tools/firmware/hvmloader/e820.c > > +++ b/tools/firmware/hvmloader/e820.c > > @@ -210,6 +210,10 @@ int build_e820_table(struct e820entry *e820, > > * space reuse by an ACPI unaware / buggy bootloader, option ROM, etc. > > * before an ACPI OS takes control. This is possible due to the fact > > that > > * ACPI NVS memory is explicitly described as non-reclaimable in ACPI > > spec. > > + * > > + * Furthermore, Xen relies on accessing ACPI tables from within the AML > > + * code exposed to guests. So Xen's ACPI tables are not, in general, > > + * reclaimable. > > */ > > > > if ( acpi_enabled ) > > diff --git a/tools/libs/light/libxl_x86.c b/tools/libs/light/libxl_x86.c > > index a3164a3077fe..265da8072a59 100644 > > --- a/tools/libs/light/libxl_x86.c > > +++ b/tools/libs/light/libxl_x86.c > > @@ -742,7 +742,7 @@ static int domain_construct_memmap(libxl__gc *gc, > > e820[nr].addr = dom->acpi_modules[i].guest_addr_out & > > ~(page_size - 1); > > e820[nr].size = dom->acpi_modules[i].length + > > (dom->acpi_modules[i].guest_addr_out & (page_size - 1)); > > - e820[nr].type = E820_ACPI; > > + e820[nr].type = E820_NVS; > > This likely needs a comment then, too. Fair enough. Let me send a v2 with that. > > Jan Cheers, Alejandro
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