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From 4ee1df89d9c92609e5fff3c9b261ce4b1bb88e42 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Wed, 26 Jun 2024 13:43:19 +0200
Subject: [PATCH 33/56] x86/xstate: Fix initialisation of XSS cache
The clobbering of this_cpu(xcr0) and this_cpu(xss) to architecturally invalid
values is to force the subsequent set_xcr0() and set_msr_xss() to reload the
hardware register.
While XCR0 is reloaded in xstate_init(), MSR_XSS isn't. This causes
get_msr_xss() to return the invalid value, and logic of the form:
old = get_msr_xss();
set_msr_xss(new);
...
set_msr_xss(old);
to try and restore said invalid value.
The architecturally invalid value must be purged from the cache, meaning the
hardware register must be written at least once. This in turn highlights that
the invalid value must only be used in the case that the hardware register is
available.
Fixes: f7f4a523927f ("x86/xstate: reset cached register values on resume")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 9e6dbbe8bf400aacb99009ddffa91d2a0c312b39
master date: 2024-06-19 13:00:06 +0100
---
xen/arch/x86/xstate.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index f442610fc5..ca76f98fe2 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -641,13 +641,6 @@ void xstate_init(struct cpuinfo_x86 *c)
return;
}
- /*
- * Zap the cached values to make set_xcr0() and set_msr_xss() really
- * write it.
- */
- this_cpu(xcr0) = 0;
- this_cpu(xss) = ~0;
-
cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
feature_mask = (((u64)edx << 32) | eax) & XCNTXT_MASK;
BUG_ON(!valid_xcr0(feature_mask));
@@ -657,8 +650,19 @@ void xstate_init(struct cpuinfo_x86 *c)
* Set CR4_OSXSAVE and run "cpuid" to get xsave_cntxt_size.
*/
set_in_cr4(X86_CR4_OSXSAVE);
+
+ /*
+ * Zap the cached values to make set_xcr0() and set_msr_xss() really write
+ * the hardware register.
+ */
+ this_cpu(xcr0) = 0;
if ( !set_xcr0(feature_mask) )
BUG();
+ if ( cpu_has_xsaves )
+ {
+ this_cpu(xss) = ~0;
+ set_msr_xss(0);
+ }
if ( bsp )
{
--
2.45.2
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