From: Jan Beulich Date: Mon, 18 Mar 2019 16:05:07 +0000 (+0100) Subject: x86/mm: fix #GP(0) in switch_cr3_cr4() X-Git-Tag: archive/raspbian/4.11.3+24-g14b62ab3e5-1+rpi1~1^2~59^2~13 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=dd32dab37487281ec688e723290a6df8cf3610d6;p=xen.git x86/mm: fix #GP(0) in switch_cr3_cr4() With "pcid=no-xpti" and opposite XPTI settings in two 64-bit PV domains (achievable with one of "xpti=no-dom0" or "xpti=no-domu"), switching from a PCID-disabled to a PCID-enabled 64-bit PV domain fails to set CR4.PCIDE in time, as CR4.PGE would not be set in either (see pv_fixup_guest_cr4(), in particular as used by write_ptbase()), and hence the early CR4 write would be skipped. Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper master commit: fdc2056767ba74346dfd8bbe868bb22521ba1418 master date: 2019-03-05 17:02:36 +0100 --- diff --git a/xen/arch/x86/flushtlb.c b/xen/arch/x86/flushtlb.c index 2f1899277c..fc4c29ca97 100644 --- a/xen/arch/x86/flushtlb.c +++ b/xen/arch/x86/flushtlb.c @@ -112,6 +112,7 @@ void switch_cr3_cr4(unsigned long cr3, unsigned long cr4) write_cr4(old_cr4); } else if ( use_invpcid ) + { /* * Flushing the TLB via INVPCID is necessary only in case PCIDs are * in use, which is true only with INVPCID being available. @@ -122,6 +123,19 @@ void switch_cr3_cr4(unsigned long cr3, unsigned long cr4) */ invpcid_flush_all_nonglobals(); + /* + * CR4.PCIDE needs to be set before the CR3 write below. Otherwise + * - the CR3 write will fault when CR3.NOFLUSH is set (which is the + * case normally), + * - the subsequent CR4 write will fault if CR3.PCID != 0. + */ + if ( (old_cr4 & X86_CR4_PCIDE) < (cr4 & X86_CR4_PCIDE) ) + { + write_cr4(cr4); + old_cr4 = cr4; + } + } + /* * If we don't change PCIDs, the CR3 write below needs to flush this very * PCID, even when a full flush was performed above, as we are currently