Re: [libvirt PATCH v2 09/12] qemu: report max number of SEV guests
On Fri, Dec 10, 2021 at 11:37:32 +0000, Daniel P. Berrangé wrote:
Different CPU generations have different limits on the number
of SEV/SEV-ES guests that can be run. Since both limits come
from the same overall set, there is typically also BIOS config
to set the tradeoff betweeen SEV and SEV-ES guest limits.
This is important information to expose for a mgmt application
scheduling guests to hosts.
Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com>
---
src/qemu/qemu_capabilities.c | 38 +++++++++++++++++++
src/qemu/qemu_driver.c | 10 +++++
.../domaincapsdata/qemu_2.12.0-q35.x86_64.xml | 2 +-
.../domaincapsdata/qemu_2.12.0-tcg.x86_64.xml | 2 +-
tests/domaincapsdata/qemu_2.12.0.x86_64.xml | 2 +-
.../domaincapsdata/qemu_6.0.0-q35.x86_64.xml | 2 +-
.../domaincapsdata/qemu_6.0.0-tcg.x86_64.xml | 2 +-
tests/domaincapsdata/qemu_6.0.0.x86_64.xml | 2 +-
8 files changed, 54 insertions(+), 6 deletions(-)
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 4ffd0a98a2..456ce1b72e 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -1897,6 +1897,8 @@ virQEMUCapsSEVInfoCopy(virSEVCapability **dst,
tmp->cbitpos = src->cbitpos;
tmp->reduced_phys_bits = src->reduced_phys_bits;
+ tmp->max_guests = src->max_guests;
+ tmp->max_es_guests = src->max_es_guests;
*dst = g_steal_pointer(&tmp);
return 0;
@@ -3286,6 +3288,30 @@ virQEMUCapsProbeQMPGICCapabilities(virQEMUCaps *qemuCaps,
}
+static void
+virQEMUCapsGetSEVMaxGuests(virSEVCapability *caps)
+{
+# if __x86_64__
cppi: /home/pipo/libvirt/src/qemu/qemu_capabilities.c: line 3294: not properly indented
+ uint32_t eax, ebx, ecx, edx;
+ asm("xor %%ebx, %%ebx;" /* clear the other registers as some cpuid */
+ "xor %%edx, %%edx;" /* functions may use them as additional arguments
*/
+ "cpuid;"
+ : "=a" (eax),
+ "=b" (ebx),
Since the code doesn't use 'eax' and 'ebx' you can remove it and add
it
to the clobbers section along with "cc".
+ "=c" (ecx),
+ "=d" (edx)
+ : "0" (0x8000001F),
+ "c" (0)
+ : "cc");
+
A comment what the data in 'ecx' and 'edx' is would be helpful even when
it's obvious on a second look
+ caps->max_guests = ecx - edx + 1;
+ caps->max_es_guests = edx - 1;
+# else
+ VIR_WARN("Unexpectedly asked for SEV guest count on non-x86_64 arch");
+ caps->max_guests = caps->max_es_guests = 0;
+# endif
+}
+
static int
virQEMUCapsProbeQMPSEVCapabilities(virQEMUCaps *qemuCaps,
qemuMonitor *mon)
@@ -3305,6 +3331,8 @@ virQEMUCapsProbeQMPSEVCapabilities(virQEMUCaps *qemuCaps,
return 0;
}
+ virQEMUCapsGetSEVMaxGuests(caps);
This code ...
+
virSEVCapabilitiesFree(qemuCaps->sevCapabilities);
qemuCaps->sevCapabilities = caps;
return 0;
@@ -4084,6 +4112,14 @@ virQEMUCapsParseSEVInfo(virQEMUCaps *qemuCaps, xmlXPathContextPtr
ctxt)
return -1;
}
+
+ /* We probe this every time because the values
+ * can change on every reboot via firmware
+ * config tunables. It is cheap to query so
+ * lack of caching is a non-issue
+ */
+ virQEMUCapsGetSEVMaxGuests(sev);
... and this code is executed also in context of e.g.
qemudomaincapstest, so the results are changing based on where you run
it, e.g. as on my box:
- <maxGuests>15</maxGuests>
+ <maxGuests>509</maxGuests>
So this method definitely is not suitable for implementation as in this
patch.
Since we already have code digging trhough 'cpuid' it feels that it
should be a better place to do so.