Commit 0cb6f412 authored by Xin Li (Intel)'s avatar Xin Li (Intel) Committed by Ingo Molnar
Browse files

x86/xen/msr: Remove calling native_{read,write}_msr{,_safe}() in pmu_msr_{read,write}() 

hpa found that pmu_msr_write() is actually a completely pointless
function:

  https://lore.kernel.org/lkml/0ec48b84-d158-47c6-b14c-3563fd14bcc4@zytor.com/



all it does is shuffle some arguments, then calls pmu_msr_chk_emulated()
and if it returns true AND the emulated flag is clear then does
*exactly the same thing* that the calling code would have done if
pmu_msr_write() itself had returned true.

And pmu_msr_read() does the equivalent stupidity.

Remove the calls to native_{read,write}_msr{,_safe}() within
pmu_msr_{read,write}().  Instead reuse the existing calling code
that decides whether to call native_{read,write}_msr{,_safe}() based
on the return value from pmu_msr_{read,write}().  Consequently,
eliminate the need to pass an error pointer to pmu_msr_{read,write}().

While at it, refactor pmu_msr_write() to take the MSR value as a u64
argument, replacing the current dual u32 arguments, because the dual
u32 arguments were only used to call native_write_msr{,_safe}(), which
has now been removed.

Suggested-by: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: default avatarXin Li (Intel) <xin@zytor.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20250427092027.1598740-11-xin@zytor.com
parent 3204877d

arch/x86/xen/enlighten_pv.c

+6 −2
Original line number Diff line number Diff line
@@ -1091,7 +1091,7 @@ static u64 xen_do_read_msr(unsigned int msr, int *err) 
{

	u64 val = 0;	/* Avoid uninitialized value for safe variant. */



	if (pmu_msr_read(msr, &val, err))

	if (pmu_msr_read_emulated(msr, &val))

		return val;



	if (err)
@@ -1133,6 +1133,8 @@ static void set_seg(unsigned int which, unsigned int low, unsigned int high, 
static void xen_do_write_msr(unsigned int msr, unsigned int low,

			     unsigned int high, int *err)

{

	u64 val;



	switch (msr) {

	case MSR_FS_BASE:

		set_seg(SEGBASE_FS, low, high, err);
@@ -1159,7 +1161,9 @@ static void xen_do_write_msr(unsigned int msr, unsigned int low, 
		break;



	default:

		if (!pmu_msr_write(msr, low, high, err)) {

		val = (u64)high << 32 | low;



		if (!pmu_msr_write_emulated(msr, val)) {

			if (err)

				*err = native_write_msr_safe(msr, low, high);

			else

arch/x86/xen/pmu.c

+4 −23
Original line number Diff line number Diff line
@@ -314,37 +314,18 @@ static bool pmu_msr_chk_emulated(unsigned int msr, uint64_t *val, bool is_read, 
	return true;

}



bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err)

bool pmu_msr_read_emulated(u32 msr, u64 *val)

{

	bool emulated;



	if (!pmu_msr_chk_emulated(msr, val, true, &emulated))

		return false;



	if (!emulated) {

		*val = err ? native_read_msr_safe(msr, err)

			   : native_read_msr(msr);

	}



	return true;

	return pmu_msr_chk_emulated(msr, val, true, &emulated) && emulated;

}



bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err)

bool pmu_msr_write_emulated(u32 msr, u64 val)

{

	uint64_t val = ((uint64_t)high << 32) | low;

	bool emulated;



	if (!pmu_msr_chk_emulated(msr, &val, false, &emulated))

		return false;



	if (!emulated) {

		if (err)

			*err = native_write_msr_safe(msr, low, high);

		else

			native_write_msr(msr, low, high);

	}



	return true;

	return pmu_msr_chk_emulated(msr, &val, false, &emulated) && emulated;

}



static u64 xen_amd_read_pmc(int counter)

arch/x86/xen/xen-ops.h

+2 −2
Original line number Diff line number Diff line
@@ -271,8 +271,8 @@ void xen_pmu_finish(int cpu); 
static inline void xen_pmu_init(int cpu) {}

static inline void xen_pmu_finish(int cpu) {}

#endif

bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err);

bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err);

bool pmu_msr_read_emulated(u32 msr, u64 *val);

bool pmu_msr_write_emulated(u32 msr, u64 val);

int pmu_apic_update(uint32_t reg);

u64 xen_read_pmc(int counter);