linux-kernel - [PATCH 3/5] x86/pvh: Set phys_base when calling xen_prepare

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Message-ID: <20240410194850.39994-4-jason.andryuk@amd.com>
Date: Wed, 10 Apr 2024 15:48:48 -0400
From: Jason Andryuk <jason.andryuk@....com>
To: Juergen Gross <jgross@...e.com>, Boris Ostrovsky
	<boris.ostrovsky@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, "Ingo
 Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>, Stefano Stabellini <sstabellini@...nel.org>, "Oleksandr
 Tyshchenko" <oleksandr_tyshchenko@...m.com>, Paolo Bonzini
	<pbonzini@...hat.com>
CC: <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>, "Jason
 Andryuk" <jason.andryuk@....com>
Subject: [PATCH 3/5] x86/pvh: Set phys_base when calling xen_prepare_pvh()

phys_base needs to be set for __pa() to work in xen_pvh_init() when
finding the hypercall page.  Set it before calling into
xen_prepare_pvh(), which calls xen_pvh_init().  Clear it afterward to
avoid __startup_64() adding to it and creating an incorrect value.

Signed-off-by: Jason Andryuk <jason.andryuk@....com>
---
Instead of setting and clearing phys_base, a dedicated variable could be
used just for the hypercall page.  Having phys_base set properly may
avoid further issues if the use of phys_base or __pa() grows.
---
 arch/x86/platform/pvh/head.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index bb1e582e32b1..c08d08d8cc92 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -125,7 +125,17 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
 	xor %edx, %edx
 	wrmsr
 
+	/* Calculate load offset from LOAD_PHYSICAL_ADDR and store in
+	 * phys_base.  __pa() needs phys_base set to calculate the
+	 * hypercall page in xen_pvh_init(). */
+	movq %rbp, %rbx
+	subq $LOAD_PHYSICAL_ADDR, %rbx
+	movq %rbx, phys_base(%rip)
 	call xen_prepare_pvh
+	/* Clear phys_base.  __startup_64 will *add* to its value,
+	 * so reset to 0. */
+	xor  %rbx, %rbx
+	movq %rbx, phys_base(%rip)
 
 	/* startup_64 expects boot_params in %rsi. */
 	lea rva(pvh_bootparams)(%ebp), %rsi
-- 
2.44.0