[PATCH] hw/i386: fix phys-bits on cpus with AMD SEV/SMD

["Jörg Thalheim" <joerg@thalheim.io>]

On AMD machines with SEV/SMD the physical address space needs
to be reduced by a number of bits. Linux does this correctly
and shows this information in /proc/cpuinfo. CPUID set by qemu
however reports too big physical addresses i.e. 48 bit instead of 43.

This patch has been tested on both Intel and AMD.

Signed-off-by: Jörg Thalheim <joerg@thalheim.io>
---
target/i386/host-cpu.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/target/i386/host-cpu.c b/target/i386/host-cpu.c
index 4ea9e354ea..0fb98ca566 100644
--- a/target/i386/host-cpu.c
+++ b/target/i386/host-cpu.c
@@ -13,22 +13,39 @@
#include "qapi/error.h"
#include "sysemu/sysemu.h"

+static uint32_t sme_sev_bits(void) {
+ uint32_t eax, ebx;
+ // get AMD Encrypted Memory Capabilities information according to AMD doc 24594—Rev. 3.32
+ host_cpuid(0x8000001f, 0, &eax, &ebx, NULL, NULL);
+ // bits:
+ // 0:1 SME
+ // 1:2 SEV
+ // ...
+ if (eax & 1 || eax & 2) {
+ // bits:
+ // 11:6 PhysAddrReduction
+ return (ebx >> 6) & 0x3f;
+ } else {
+ return 0;
+ }
+}
+
/* Note: Only safe for use on x86(-64) hosts */
static uint32_t host_cpu_phys_bits(void)
{
- uint32_t eax;
+ uint32_t eax, ebx;
uint32_t host_phys_bits;

host_cpuid(0x80000000, 0, &eax, NULL, NULL, NULL);
if (eax >= 0x80000008) {
- host_cpuid(0x80000008, 0, &eax, NULL, NULL, NULL);
+ host_cpuid(0x80000008, 0, &eax, &ebx, NULL, NULL);
/*
* Note: According to AMD doc 25481 rev 2.34 they have a field
* at 23:16 that can specify a maximum physical address bits for
* the guest that can override this value; but I've not seen
* anything with that set.
*/
- host_phys_bits = eax & 0xff;
+ host_phys_bits = (eax & 0xff) - sme_sev_bits();
} else {
/*
* It's an odd 64 bit machine that doesn't have the leaf for
-- 
2.32.0