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From 54102e428ba3f677904278479f8110c8eef6fedc Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Tue, 21 Mar 2023 13:53:25 +0100
Subject: [PATCH 46/61] libacpi: fix PCI hotplug AML
The emulated PIIX3 uses a nybble for the status of each PCI function,
so the status for e.g. slot 0 functions 0 and 1 respectively can be
read as (\_GPE.PH00 & 0x0F), and (\_GPE.PH00 >> 0x04).
The AML that Xen gives to a guest gets the operand order for the odd-
numbered functions the wrong way round, returning (0x04 >> \_GPE.PH00)
instead.
As far as I can tell, this was the wrong way round in Xen from the
moment that PCI hotplug was first introduced in commit 83d82e6f35a8:
+ ShiftRight (0x4, \_GPE.PH00, Local1)
+ Return (Local1) /* IN status as the _STA */
Or maybe there's bizarre AML operand ordering going on there, like
Intel's wrong-way-round assembler, and it only broke later when it was
changed to being generated?
Either way, it's definitely wrong now, and instrumenting a Linux guest
shows that it correctly sees _STA being 0x00 in function 0 of an empty
slot, but then the loop in acpiphp_glue.c::get_slot_status() goes on to
look at function 1 and sees that _STA evaluates to 0x04. Thus reporting
an adapter is present in every slot in /sys/bus/pci/slots/*
Quite why Linux wants to look for function 1 being physically present
when function 0 isn't... I don't want to think about right now.
Fixes: 83d82e6f35a8 ("hvmloader: pass-through: multi-function PCI hot-plug")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: b190af7d3e90f58da5f58044b8dea7261b8b483d
master date: 2023-03-20 17:12:34 +0100
---
tools/libacpi/mk_dsdt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/libacpi/mk_dsdt.c b/tools/libacpi/mk_dsdt.c
index c5ba4c0b2f..250a50b7eb 100644
--- a/tools/libacpi/mk_dsdt.c
+++ b/tools/libacpi/mk_dsdt.c
@@ -431,7 +431,7 @@ int main(int argc, char **argv)
stmt("Store", "0x89, \\_GPE.DPT2");
}
if ( slot & 1 )
- stmt("ShiftRight", "0x4, \\_GPE.PH%02X, Local1", slot & ~1);
+ stmt("ShiftRight", "\\_GPE.PH%02X, 0x04, Local1", slot & ~1);
else
stmt("And", "\\_GPE.PH%02X, 0x0f, Local1", slot & ~1);
stmt("Return", "Local1"); /* IN status as the _STA */
--
2.40.0
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